Ask ten people what a person of your height "should" weigh and you will get ten answers. Ask four published medical formulas and you will get four different numbers, sometimes eight kilograms apart. That is not a flaw in your body. It is a flaw in the question.
The phrase ideal weight sounds like it describes a fact about you, the way your shoe size does. It does not. It describes the output of an equation that someone wrote down for a specific purpose, in a specific decade, for a specific reason that usually had nothing to do with health. Once you know where those equations came from, the calculator on this page stops being a verdict and becomes what it actually is: a rough map with several roads drawn on it, useful precisely because it shows you how much the roads disagree.
This guide covers all of it. The history behind the numbers, the arithmetic you can do on paper, the reference tables you can bookmark, and the one measurement that research consistently shows beats body mass index at predicting whether your body is heading for trouble. There is a lot here, so use the list below to jump around. If you only want the BMI formula itself — the full history, the Asia-Pacific thresholds, BMI Prime, and the Ponderal Index — that is covered in depth in our separate BMI Calculator guide; this article builds on top of it.
Ideal Weight Calculator Embed Code for Your Website:
You have just read through the full story of this tool — the four formulas (Robinson, Miller, Hamwi, and Devine) that each give you a different number, sometimes eight kilograms apart, because they were written in different decades for different populations and different purposes; the healthy BMI range that spans from 18.5 to 24.9 and provides a band rather than a single verdict; the waist‑to‑height ratio that research consistently shows outperforms BMI for predicting cardiometabolic risk; and the honest explanation of why the phrase "ideal weight" describes the output of an equation rather than a fact about you. You have seen the history of the Metropolitan Life tables, the arithmetic you can do on paper, the reference tables you can bookmark, and the quiet insistence on zero ads, zero sign‑ups, and zero data collection. Now comes the practical part: putting that same engine onto your own site, so your visitors can calculate their numbers without ever leaving your pages.
You can copy the code below and embed it on your website — in articles, sidebars, footers, or anywhere you want visitors to access a clinically grounded weight calculator. The tool runs entirely in the browser, inside an isolated container that cannot read or touch the page around it. No personal data — no height, no weight, no waist circumference — is transmitted, stored, or logged. All calculations happen locally on your visitor's own device. The four formulas, the BMI range calculation, the waist‑to‑height ratio assessment, the frame‑size adjustment, and the interpretation of what the numbers actually mean all work without a single server round‑trip. Close the tab and the entire session evaporates. What your visitors calculate stays with them, which is exactly how a weight calculator should work — it is not the number that matters, but the understanding and perspective the numbers give to the person reading them.
The embed is available in six interface languages to match your audience: English - Spanish - French - Arabic - Chinese - Hindi. The language setting controls the tool's labels, buttons, and instructions — and also determines which language the results, the formula descriptions, and the health‑risk explanations appear in. The calculator itself is the same for every visitor worldwide, but the language it displays in is entirely your visitor's choice, detected automatically from their browser on first visit and remembered afterward. For Arabic, the entire layout flips to right‑to‑left, mirroring the interface so the experience feels native.
Switch the interface language by changing the parameter in the URL: ?lang=en
Available languages: en - es - fr - ar - zh - hi
1- Isolated iFrame Code (Ideal for Articles and Pages):
If you are publishing a guide, a deep‑dive article about weight and health, or a resource for people trying to understand their numbers — exactly like the one you are reading now — this method drops the fully functional calculator directly into the flow of your content. The isolated iframe keeps the tool contained, so your layout stays clean and your readers can calculate their ideal weight range, explore the four formulas, and check their waist‑to‑height ratio without reloading the page. Every feature works exactly as described: the four formulas with their respective equations and histories, the healthy BMI band, the waist‑to‑height ratio assessment, the frame‑size adjustment, and the interpretation of what the numbers actually mean — all inside a small, self‑contained room on your site.
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2- Flexible Script (Suitable for Sidebars and Templates):
For sidebars, footers, or widget areas, this lighter integration loads the calculator on demand and adjusts to its container. It is the same engine, same four formulas, same healthy BMI band, same waist‑to‑height ratio assessment, same frame‑size adjustment, same six‑language support — just packaged for places where an iframe might feel heavy. Drop it into your template, and the calculator appears where you want it, when you want it. Your visitors can calculate their ideal weight range, compare the four formulas, and check their waist‑to‑height ratio without ever leaving your site.
<div class="tooliqo-tool" data-tool="ideal-weight-calculator" data-lang="en"></div><script src="https://tools.tooliqo.co/embed.js" async></script>
Note: Both methods load the same calculator — the one whose four formulas, healthy BMI band, waist‑to‑height ratio assessment, frame‑size adjustment, and six languages you have just read about. The tool respects dark mode and reduced‑motion settings on your visitors' devices. No watermarks, no daily limits, no data collection. Just the calculator, doing what it does, on your site. And if a visitor enters their height, sees the four different numbers side by side, and finally understands why every source they have ever checked gave them a different answer — the tool has done what it was built to do. The rest is up to them, which was always the point.
What this guide covers
- What "ideal weight" actually means
- The four formulas, and what they were really built for
- Why the four formulas disagree, and by exactly how much
- The hidden flaw: linear formulas describing a squared body
- Body mass index in one minute (and where the four formulas are checked against it)
- Your healthy weight range, by height
- Waist-to-height ratio: the measure that outperforms BMI
- Body frame size: a useful idea on weak evidence
- How age changes everything
- Ethnicity and the shifted thresholds
- Conversion formulas and quick reference tables
- How to use the calculator on this page
- Three worked examples
- What predicts health better than the scale
- Frequently asked questions
- When to speak to a professional
What "ideal weight" actually means
The concept has a paper trail, and it starts in an unexpected place: an insurance office in New York.
The insurance-company origin
In the early 1940s, a statistician named Louis Dublin was working as an actuary at the Metropolitan Life Insurance Company. His job was not to keep anyone healthy. His job was to work out which policyholders were likely to die sooner, so the company could price its premiums correctly. Dublin had access to something almost nobody else did at the time: height and weight records for millions of insured people, matched against how long they subsequently lived.
He sorted the data and published tables of "ideal" weights for each height. Later editions softened the word to "desirable." Those tables, revised in 1959 and again in 1983, quietly became the reference standard for doctors, dietitians, magazines, and eventually every weight chart taped inside a gym locker for the next half century.
It is worth sitting with what that data actually was. Metropolitan Life policyholders were not a cross-section of humanity. They were disproportionately white, urban, middle-class, and employed, because those were the people who bought life insurance. Many were weighed wearing shoes and street clothes. Some heights were self-reported, and people round their own height upward with remarkable consistency. The tables also divided people into small, medium, and large frames, but the original publications did not always explain how to determine which frame you had, which meant readers picked whichever column produced a number they liked.
None of this made the tables useless. They captured something real, which is that at the population level, being substantially heavier or lighter than average for your height correlated with dying earlier. But they were never a biological measurement of an individual person's correct mass, and they were never presented as one by the actuaries who built them.
Why the phrase survived anyway
"Ideal weight" survived because it is enormously convenient. A single number is easy to print, easy to remember, easy to aim at. A range is harder to sell. A statement like "the healthiest weight for you depends on your muscle mass, fat distribution, ancestry, age, fitness, sleep, blood pressure, and family history, and can only be sensibly interpreted by someone who has examined you" is accurate and completely useless on a magazine cover.
So the number stayed. And because it stayed, millions of people have measured themselves against a figure that was originally a byproduct of insurance pricing.
The four formulas, and what they were really built for
The calculator on this page runs four named equations. Every serious ideal-weight tool uses some subset of these. Almost none of them tell you what the equations were written for, which is the single most clarifying fact about them.
Hamwi, 1964
Dr. George Hamwi was an endocrinologist. He published his rule in a text on diagnosing and treating diabetes mellitus, and he needed it for one reason: planning meals for diabetic patients at the bedside. In 1964, a doctor on a ward round did not have a calculator, let alone a chart. Hamwi needed something he could do in his head in five seconds while standing next to a patient. So he anchored it at five feet and added a flat amount per inch above that. Simple, fast, and designed for clinical dietary planning, not for telling people what to weigh.
Devine, 1974
This is the one that ended up everywhere, and its origin is the most surprising of the four. B.J. Devine published it in a clinical pharmacy journal in a paper about gentamicin therapy. Gentamicin is a powerful antibiotic with a narrow safety margin, capable of damaging the kidneys and inner ear if the dose is too high. Fat tissue does not take up the drug the way lean tissue does, so dosing by total body weight overdoses heavier patients. Devine needed a quick estimate of lean body size to scale the dose.
He proposed his equation, by his own account, as a practical starting point rather than a validated measurement. It was never tested as a health target. It has since been used to dose thousands of medications, calculate ventilator tidal volumes, and, entirely by accident, to tell people on the internet what they should weigh.
Robinson and Miller, both 1983
Nearly a decade later, two separate groups working in hospital pharmacy published revisions in the same year and the same field. Robinson and colleagues recalibrated Devine's equation against the Metropolitan Life tables. Miller and colleagues produced their own variant. Both were explicitly aimed at drug dosage calculation. Both flattened the per-inch increment, Miller most aggressively, which turns out to matter a great deal, as the next section shows.
| Formula | Year | Male | Female | Original purpose |
|---|---|---|---|---|
| Hamwi | 1964 | 48.0 + 2.7 per inch over 5 ft | 45.5 + 2.2 per inch over 5 ft | Bedside diet planning in diabetes care |
| Devine | 1974 | 50.0 + 2.3 per inch over 5 ft | 45.5 + 2.3 per inch over 5 ft | Gentamicin antibiotic dosing |
| Robinson | 1983 | 52.0 + 1.9 per inch over 5 ft | 49.0 + 1.7 per inch over 5 ft | Drug dosage calculation |
| Miller | 1983 | 56.2 + 1.41 per inch over 5 ft | 53.1 + 1.36 per inch over 5 ft | Drug dosage calculation |
Notice the pattern in the two columns. The base value climbs from 48 to 56.2 kilograms as you move down the list, while the per-inch increment falls from 2.7 to 1.41. Each successive author started higher and rose more slowly. That single design decision is the source of nearly all the disagreement between them.
Why the four formulas disagree, and by exactly how much
Here is something most ideal-weight articles never show you: the actual spread between the four equations at different heights. It is not constant. It collapses to almost nothing near average height and blows open at both extremes.
| Height | Hamwi | Devine | Robinson | Miller | Spread | Healthy BMI range |
|---|---|---|---|---|---|---|
| Male, 155 cm | 50.8 | 52.4 | 53.9 | 57.6 | 6.9 kg | 44.4 to 59.8 |
| Male, 165 cm | 61.4 | 61.4 | 61.4 | 63.2 | 1.8 kg | 50.4 to 67.8 |
| Male, 175 cm | 72.0 | 70.5 | 68.9 | 68.7 | 3.3 kg | 56.7 to 76.3 |
| Male, 185 cm | 82.7 | 79.5 | 76.4 | 74.3 | 8.4 kg | 63.3 to 85.2 |
| Female, 155 cm | 47.8 | 47.9 | 50.7 | 54.5 | 6.7 kg | 44.4 to 59.8 |
| Female, 165 cm | 56.4 | 56.9 | 57.4 | 59.8 | 3.4 kg | 50.4 to 67.8 |
| Female, 175 cm | 65.1 | 66.0 | 64.1 | 65.2 | 1.8 kg | 56.7 to 76.3 |
| Female, 185 cm | 73.7 | 75.0 | 70.8 | 70.6 | 4.5 kg | 63.3 to 85.2 |
Look at the 165 cm male row. All four formulas land within 1.8 kg of each other, which feels like scientific consensus. Now look at the 185 cm male row: 8.4 kg of disagreement, roughly the weight of a large watermelon. Same equations, same person type, wildly different confidence.
The reason is that all four were calibrated against populations clustered around average height. Near the middle of the distribution they agree because they were all fitted to the same middle. Away from it, each author's arbitrary choice of slope takes over and they fan apart. If you are notably short or notably tall, the four formulas are not four independent confirmations of your ideal weight. They are four extrapolations, and they are guessing.
The hidden flaw: linear formulas describing a squared body
This section is the one that changed how I read these numbers, and I have not seen it explained clearly anywhere else, so here it is in full.
Body mass index divides weight by height squared. That squaring is not decoration. It is an attempt to reflect a geometric truth: when a body gets taller, it also gets wider and deeper. Mass scales faster than height does.
All four ideal weight formulas are linear. They add a fixed number of kilograms per inch, forever, at every height. A linear equation cannot track a squared relationship. So as height moves away from the calibration point, the formulas drift, and you can see the drift by asking a simple question: what BMI does each formula's answer actually correspond to?
| Height | Hamwi | Devine | Robinson | Miller |
|---|---|---|---|---|
| 150 cm | 20.2 | 21.3 | 22.3 | 24.4 |
| 160 cm | 21.9 | 22.2 | 22.5 | 23.6 |
| 170 cm | 23.1 | 22.8 | 22.5 | 22.8 |
| 180 cm | 23.9 | 23.1 | 22.4 | 22.1 |
| 190 cm | 24.4 | 23.3 | 22.2 | 21.3 |
| 200 cm | 24.6 | 23.3 | 21.9 | 20.7 |
Read the Miller column from top to bottom. For a 150 cm man it recommends a weight equivalent to BMI 24.4, which sits at the very top of the healthy band. For a 200 cm man it recommends BMI 20.7, near the bottom. That is a swing of almost four BMI points produced by nothing but the arithmetic. Miller did not decide that very tall men should be leaner. The straight line simply fell behind the curve.
Now read the Hamwi column. It does the exact opposite, climbing from 20.2 to 24.6. Hamwi's steeper slope overshoots as height increases.
The practical takeaway is direct. If you are between roughly 165 and 180 cm, the four formulas are reasonably trustworthy and roughly agree. Outside that band, treat them as historical curiosities and use your healthy BMI range instead, because the range is built on the correct geometry. The calculator on this page deliberately shows the healthy range as the headline figure and the four formulas beneath it, in that order, for exactly this reason.
Body mass index in one minute
Everything above is benchmarked against BMI, so here is the version you need to follow the rest of this article. For the fuller picture — Adolphe Quetelet's original 1830s index, how Ancel Keys turned it into a clinical standard in 1972, the Asia-Pacific thresholds, and the BMI Prime and Ponderal Index variants — see our dedicated BMI Calculator guide, which covers all of it in depth.
Metric: weight in kilograms ÷ (height in metres × height in metres). So 72 kg at 1.75 m gives 72 ÷ 3.0625 = 23.5.
Imperial: 703 × weight in pounds ÷ (height in inches × height in inches). So 160 lb at 69 inches gives 703 × 160 ÷ 4761 = 23.6.
| Category | BMI |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5 to 24.9 |
| Overweight | 25.0 to 29.9 |
| Obesity, class I | 30.0 to 34.9 |
| Obesity, class II | 35.0 to 39.9 |
| Obesity, class III | 40.0 and above |
These boundaries are round numbers, and that is not an accident — nothing biological happens crossing from 24.9 to 25.0. The cut points were chosen because population data showed risk beginning to rise in those neighbourhoods and because clean thresholds are usable in clinical practice.
The one thing worth carrying into the rest of this article: BMI cannot separate muscle from fat, says nothing about where fat sits on the body, and needs different rules entirely for children, pregnancy, and adults over 65. The three worked examples further down show exactly how much that matters in practice. For the full list of where BMI breaks down, the Asia-Pacific thresholds, and the two lesser-known variants — BMI Prime and the Ponderal Index — see the BMI Calculator guide.
Your healthy weight range, by height
If you take one table away from this article, take this one. It is your body's healthy weight band, derived by rearranging the BMI equation to solve for weight at the boundaries 18.5 and 24.9 — the same range worked out in full in our BMI guide, reproduced here so you can compare it directly against the four formulas above.
The arithmetic, if you want to do it yourself:
- Lower limit in kilograms = 18.5 × height in metres × height in metres
- Upper limit in kilograms = 24.9 × height in metres × height in metres
| Height (cm) | Height (ft, in) | Healthy range (kg) | Healthy range (lb) |
|---|---|---|---|
| 145 | 4 ft 9 in | 38.9 to 52.4 | 86 to 115 |
| 150 | 4 ft 11 in | 41.6 to 56.0 | 92 to 124 |
| 155 | 5 ft 1 in | 44.4 to 59.8 | 98 to 132 |
| 160 | 5 ft 3 in | 47.4 to 63.7 | 104 to 141 |
| 165 | 5 ft 5 in | 50.4 to 67.8 | 111 to 149 |
| 170 | 5 ft 7 in | 53.5 to 72.0 | 118 to 159 |
| 175 | 5 ft 9 in | 56.7 to 76.3 | 125 to 168 |
| 180 | 5 ft 11 in | 59.9 to 80.7 | 132 to 178 |
| 185 | 6 ft 1 in | 63.3 to 85.2 | 140 to 188 |
| 190 | 6 ft 3 in | 66.8 to 89.9 | 147 to 198 |
| 195 | 6 ft 5 in | 70.3 to 94.7 | 155 to 209 |
| 200 | 6 ft 7 in | 74.0 to 99.6 | 163 to 220 |
Two things about this table deserve emphasis.
First, the ranges are wide. At 170 cm the healthy band spans 18.5 kilograms. That is not sloppiness. It is an honest acknowledgement that people of identical height carry legitimately different amounts of bone, muscle, and tissue. Anyone offering you a single ideal number for your height is offering false precision.
Second, the band is the same for men and women. BMI thresholds are not sex-specific, even though the four formulas are. Women on average carry a higher proportion of body fat at the same BMI, which is normal physiology, and the categories do not adjust for it. This is one of the places where the four formulas, whatever their flaws, encode something BMI does not.
Waist-to-height ratio: the measure that outperforms BMI
If you only add one new habit after reading this, make it this one. Get a tape measure and check your waist against your height.
The ratio could not be simpler. Divide your waist circumference by your height, in the same units. A 90 cm waist on a 180 cm frame gives 0.50. That is the number.
Why waist fat is different
Body fat is not one substance in one place. Subcutaneous fat sits under the skin, spread across hips, thighs, arms, and back. Visceral fat sits inside the abdominal cavity, wrapped around the liver, pancreas, and intestines. They behave differently enough that lumping them together as "fat" obscures most of what matters.
Visceral fat is metabolically active tissue. It releases free fatty acids and inflammatory signalling molecules directly into the portal vein, which delivers them straight to the liver before they reach general circulation. That direct delivery is thought to drive much of the insulin resistance, disturbed blood lipids, and low-grade chronic inflammation associated with abdominal obesity. Subcutaneous fat on the thighs does not do this to anything like the same degree, and some evidence suggests lower-body fat may even be mildly protective.
This is why two people at the same BMI can face genuinely different risks, and why a tape measure around the middle tells you something the bathroom scale structurally cannot.
What the research says
Waist-to-height ratio has been compared against BMI and against waist circumference alone in a large body of work, including meta-analyses pooling many studies and hundreds of thousands of participants. The consistent finding is that the ratio outperforms both for predicting cardiometabolic risk factors such as high blood pressure, adverse cholesterol profiles, and type 2 diabetes.
The reason it beats raw waist circumference is intuitive once stated: an 85 cm waist means something quite different on a 150 cm person than on a 195 cm person. Dividing by height normalises for body size, which is exactly what a raw circumference measurement fails to do.
The evidence has been strong enough that clinical guidance has moved. Britain's National Institute for Health and Care Excellence now recommends measuring waist-to-height ratio alongside BMI for adults, using 0.5 as the practical threshold. The public health message that came out of this line of research is memorable precisely because it needs no arithmetic at all: keep your waist to less than half your height.
How to measure your waist properly
Most people measure it wrong, and wrong measurement is worse than none because it gives you false confidence. Do this instead:
- Take the measurement against bare skin or a thin layer, never over a jumper or a belt.
- Stand upright with your feet roughly hip-width apart and your arms relaxed at your sides.
- Find the landmark. The standard clinical site is the midpoint between the bottom of your lowest rib and the top of your hip bone. Some protocols use the narrowest point of the torso, others the level of the navel. Any of these is defensible.
- Breathe out normally, then measure. Do not suck in, and do not push the tape into your skin. It should be snug enough to stay put and no tighter.
- Measure at the same time of day, ideally in the morning before eating, and use the same landmark every time. Consistency matters more than which landmark you picked.
| Ratio | Interpretation |
|---|---|
| Below 0.40 | Below the usual range; worth mentioning to a doctor |
| 0.40 to 0.49 | Healthy range |
| 0.50 to 0.59 | Increased risk |
| 0.60 and above | High risk |
To save you the arithmetic entirely, here is where the two key lines fall at each height.
| Height | 0.5 line (cm) | 0.5 line (in) | 0.6 line (cm) | 0.6 line (in) |
|---|---|---|---|---|
| 150 cm / 4 ft 11 in | 75.0 | 29.5 | 90.0 | 35.4 |
| 155 cm / 5 ft 1 in | 77.5 | 30.5 | 93.0 | 36.6 |
| 160 cm / 5 ft 3 in | 80.0 | 31.5 | 96.0 | 37.8 |
| 165 cm / 5 ft 5 in | 82.5 | 32.5 | 99.0 | 39.0 |
| 170 cm / 5 ft 7 in | 85.0 | 33.5 | 102.0 | 40.2 |
| 175 cm / 5 ft 9 in | 87.5 | 34.4 | 105.0 | 41.3 |
| 180 cm / 5 ft 11 in | 90.0 | 35.4 | 108.0 | 42.5 |
| 185 cm / 6 ft 1 in | 92.5 | 36.4 | 111.0 | 43.7 |
| 190 cm / 6 ft 3 in | 95.0 | 37.4 | 114.0 | 44.9 |
| 195 cm / 6 ft 5 in | 97.5 | 38.4 | 117.0 | 46.1 |
One caveat worth stating plainly: the 0.5 threshold is a screening line drawn largely from research in adults with a BMI below about 35, and it is not designed for use during pregnancy. Like every threshold in this article, it flags a conversation worth having, not a diagnosis.
Body frame size: a useful idea on weak evidence
The calculator includes a body frame selector, and honesty requires explaining exactly how much weight to put on it.
The underlying idea is sound. Skeletons genuinely differ. Two adults of identical height can have measurably different bone widths, and the one with the broader skeleton carries more mass at the same body fat percentage. The Metropolitan Life tables recognised this and published separate columns for small, medium, and large frames, using elbow breadth measured with callipers as the classifier.
The problem is the popular shortcut. The method you will find everywhere, including in this calculator, is to wrap your thumb and index finger around the opposite wrist: overlapping fingers mean a small frame, fingers just touching mean medium, fingers that cannot meet mean large. It is quick and it is intuitive. It is also a folk heuristic rather than a validated clinical measurement, and it is confounded by finger length, hand size, and wrist fat.
So use it, but use it lightly. In the calculator, selecting a small frame reduces each formula's output by 10 percent and a large frame increases it by 10 percent, which is the conventional adjustment. Treat that as adding a little honest fuzz to numbers that were never precise, not as refining them.
How age changes everything
Age is the variable most weight charts ignore and the one that changes the interpretation most.
Children and teenagers
Adult BMI categories should never be applied to anyone under 18. Not as a rough guide, not as a ballpark. Children's body composition changes continuously through growth, and the same BMI can be entirely healthy at nine and concerning at fifteen, or the reverse.
Instead, a child's BMI is plotted against reference charts for their exact age and sex, producing a percentile that says how they compare to other children of the same age. A percentile is a position in a distribution, not a verdict, and a single reading matters far less than the trajectory across several visits.
| Percentile | Category |
|---|---|
| Below the 5th | Underweight |
| 5th to below the 85th | Healthy weight |
| 85th to below the 95th | Overweight |
| 95th and above | Obesity |
This is why the calculator on this page changes behaviour when you enter an age under 18. It hides the four formulas and the healthy weight range entirely, shows the BMI figure without an adult category label, and points you towards a paediatrician. Showing a fifteen-year-old the word "obese" based on adult thresholds is not merely unhelpful, it is clinically incorrect, and a tool that does it is badly built.
Adults over 65
The picture genuinely shifts in later life, and in a direction that surprises people.
Several meta-analyses of older populations have found that the BMI associated with the lowest mortality sits higher than the standard healthy band, in some analyses closer to the mid-twenties through to around 30. A few mechanisms plausibly contribute. Age-related muscle loss means that maintaining weight becomes protective rather than concerning. Some reserve of tissue helps people withstand illness, surgery, and hospital stays. And in older adults, unintentional weight loss is often a signal of underlying disease rather than a health achievement.
Worth noting that the interpretation of this pattern, sometimes called the obesity paradox, is genuinely contested. Critics point out that serious illness causes weight loss, which can make lower weight look dangerous when the disease is doing the damage. Smoking history further muddies the analysis. The honest summary is that after 65 the standard thresholds become less reliable, and that muscle mass, grip strength, and physical function tell a clinician more than BMI does.
The calculator flags a note when you enter an age of 65 or over, for this reason.
Ethnicity and the shifted thresholds
A given BMI does not carry the same risk in every population, and this has real clinical consequences.
Research across South Asian, Chinese, and other East and Southeast Asian populations has repeatedly found higher body fat percentage and higher rates of type 2 diabetes and cardiovascular disease at BMI values that would be classed as healthy or merely overweight by the standard cut points. Body fat distribution differs, with a greater tendency toward abdominal and visceral deposition at a given total mass.
A World Health Organization expert consultation examined this and identified lower action points for Asian populations, with increased risk beginning around a BMI of 23 and high risk from around 27.5. Several countries have since adopted lower national thresholds, and clinical guidelines in a number of health systems now apply reduced BMI cut points when assessing people of South Asian, Chinese, other Asian, Middle Eastern, Black African, or African-Caribbean family background. For the full Asia-Pacific classification table, see our BMI Calculator guide.
The calculator applies the standard World Health Organization thresholds, because they are the internationally recognised default and because it does not ask for your ancestry. If your family background falls into any of the groups above, read your result knowing that the meaningful line for you may sit a point or two lower than the table says, and raise it with a doctor rather than adjusting anything on your own.
Conversion formulas and quick reference tables
Every unit conversion the calculator performs internally, in case you want to check its work or do the arithmetic on paper.
| Conversion | Formula | Quick mental version |
|---|---|---|
| Kilograms to pounds | kg × 2.20462 | Double it, add 10 percent |
| Pounds to kilograms | lb ÷ 2.20462 | Halve it, subtract 10 percent |
| Centimetres to inches | cm ÷ 2.54 | Divide by 2.5 |
| Inches to centimetres | in × 2.54 | Multiply by 2.5, add a touch |
| Feet and inches to centimetres | (ft × 12 + in) × 2.54 | Total inches, then × 2.54 |
| Centimetres to feet and inches | cm ÷ 2.54, then ÷ 12 for feet, remainder is inches | — |
| Metres to feet | m × 3.28084 | Multiply by 3.28 |
| Stones to kilograms | st × 6.35029 | Multiply by 6.35 |
| BMI, metric | kg ÷ (m × m) | — |
| BMI, imperial | 703 × lb ÷ (in × in) | — |
| BMI Prime | BMI ÷ 25 | — |
| Ponderal index | kg ÷ (m × m × m) | — |
| Waist-to-height ratio | waist ÷ height, same units | Is your waist under half your height? |
| kg | lb | kg | lb |
|---|---|---|---|
| 40 | 88.2 | 100 | 220.5 |
| 45 | 99.2 | 105 | 231.5 |
| 50 | 110.2 | 110 | 242.5 |
| 55 | 121.3 | 115 | 253.5 |
| 60 | 132.3 | 120 | 264.6 |
| 65 | 143.3 | 125 | 275.6 |
| 70 | 154.3 | 130 | 286.6 |
| 75 | 165.3 | 135 | 297.6 |
| 80 | 176.4 | 140 | 308.6 |
| 85 | 187.4 | 145 | 319.7 |
| 90 | 198.4 | 150 | 330.7 |
| 95 | 209.4 | 155 | 341.7 |
| cm | Feet and inches | cm | Feet and inches |
|---|---|---|---|
| 140 | 4 ft 7.1 in | 175 | 5 ft 8.9 in |
| 145 | 4 ft 9.1 in | 180 | 5 ft 10.9 in |
| 150 | 4 ft 11.1 in | 185 | 6 ft 0.8 in |
| 155 | 5 ft 1.0 in | 190 | 6 ft 2.8 in |
| 160 | 5 ft 3.0 in | 195 | 6 ft 4.8 in |
| 165 | 5 ft 5.0 in | 200 | 6 ft 6.7 in |
| 170 | 5 ft 6.9 in | 205 | 6 ft 8.7 in |
How to use the calculator on this page
The tool works entirely inside your browser. Nothing you type is transmitted anywhere or stored, which for measurements like these seemed like the right default rather than a feature to advertise.
The inputs
- Units. Switch between metric and imperial at any time. Values you have already entered are converted rather than cleared, so you can flip between systems to sanity-check a figure.
- Sex. Required only because the four historical formulas were published with separate coefficients for male and female bodies. Your BMI, your healthy weight range, and your waist-to-height ratio are all unaffected by this selection.
- Height. Measure without shoes, standing straight against a wall, heels together, looking directly ahead. Height compresses slightly through the day, so morning readings run a few millimetres taller. Small errors here matter more than you would expect, because height is squared in the BMI calculation.
- Weight. Most consistent first thing in the morning, after using the bathroom, before eating or drinking. Day-to-day fluctuation of one to two kilograms from water, food volume, and salt intake is entirely normal and tells you nothing.
- Age, optional. Used to switch interpretation, not to alter arithmetic. Under 18 the adult formulas are suppressed; at 65 and over a note appears about shifted thresholds.
- Body frame, optional. Adjusts the four formulas by 10 percent in either direction. Read the frame section above before relying on it.
- Waist, optional. Add this. It unlocks the waist-to-height ratio, which is the most informative single output the tool produces.
Reading the results
| Output | What it is | How much to trust it |
|---|---|---|
| Healthy weight range | The weights corresponding to BMI 18.5 to 24.9 at your height | Highest. Built on the correct geometry and holds at all heights |
| The measurement scale | Your current weight plotted against that band on a marked axis | A visual restatement of the range; the position is what matters, not the exact pixel |
| BMI and category | Your ratio of weight to height squared, with the WHO band | Good as a screening figure. Poor for athletes, older adults, pregnancy, and height extremes |
| Waist-to-height ratio | Waist divided by height, with a risk band | Very high, provided you measured your waist carefully and consistently |
| Four formula results | Hamwi, Devine, Robinson, Miller, each adjusted for frame | Reasonable between roughly 165 and 180 cm. Drifts badly outside that. Historical context more than guidance |
| Average of the four | Mean of the four formulas | Smooths the disagreement but inherits every underlying flaw. Do not treat it as a target |
| BMI Prime and ponderal index | Two alternative expressions of the same measurements | Useful for perspective; the ponderal index is more informative at the height extremes |
Three worked examples
Identical BMI values, three different stories. This is the clearest demonstration of why one number cannot carry the whole load.
A 34-year-old man, 178 cm, 88 kg, waist 84 cm
His BMI is 27.8, which the WHO table calls overweight. His healthy weight range is 58.6 to 78.9 kg, so he sits about 9 kg above the top of it. On the four formulas he comes out around 71 to 76 kg, meaning he appears to be 12 to 17 kg over "ideal."
Then look at the waist. 84 divided by 178 gives 0.47, comfortably inside the healthy band, and well under half his height. He lifts four times a week and carries substantial muscle. The excess mass BMI is flagging is largely lean tissue, and the waist measurement catches what BMI missed. For him, the overweight label is close to meaningless and the ratio is the number that matters.
A 52-year-old woman, 162 cm, 65 kg, waist 89 cm
Her BMI is 24.8, sitting just inside the healthy band with 0.1 to spare. Her healthy range is 48.6 to 65.3 kg, so she is at the very top of it. All four formulas put her near 55 to 58 kg. On BMI alone, she would reasonably conclude everything is fine.
Her waist tells a different story. 89 divided by 162 gives 0.55, which lands in the increased-risk band. The distribution of her weight, concentrated abdominally, carries metabolic implications her BMI does not reveal at all. She is the case that most justifies adding the tape measure: a normal BMI with a waist that warrants a conversation and probably a blood panel.
A 71-year-old man, 170 cm, 79 kg, waist 96 cm
BMI 27.3, overweight by the standard table. Healthy range 53.5 to 72.0 kg, so 7 kg above it. His waist-to-height ratio is 0.56, in the increased-risk band.
But he is 71, and the standard thresholds are the least reliable at his age. Research in older populations suggests his BMI may sit near the range associated with the best outcomes, and any weight loss at his age would need to protect muscle rather than simply reduce the number. Meanwhile his waist ratio is still worth attention, and grip strength, walking speed, and blood pressure would tell his doctor far more than either figure. He is the clearest example of a person for whom the calculator is a starting point for a conversation and nothing more.
What predicts health better than the scale
If you want a more accurate picture of your health than any weight calculator can give you, these are the things that carry more signal. None of them require you to change anything today; they are simply the measures that a clinician weighs more heavily.
- Waist-to-height ratio. Covered at length above. Cheap, quick, and better evidenced than BMI for cardiometabolic risk.
- Cardiorespiratory fitness. Across many cohort studies, fitness is a stronger predictor of mortality than body weight, and fit people at higher body weights often show better outcomes than unfit people at lower ones.
- Blood pressure. Cheap to measure, hugely consequential, and often silent until it is not.
- Blood markers. Fasting glucose or HbA1c, and a lipid panel. These measure what is actually happening metabolically rather than inferring it from mass.
- Muscle mass and strength. Grip strength alone predicts a startling range of outcomes, particularly in older adults, and it is invisible to BMI.
- Sleep. Consistently short or disrupted sleep is associated with disturbed appetite regulation, insulin sensitivity, and cardiovascular risk. It also happens to be one of the more modifiable items on this list.
- Weight stability over years. A steady weight generally reflects a metabolically calmer state than repeated cycles of loss and regain.
- Family history. Not modifiable, but it changes how aggressively everything else should be screened.
The thread running through that list is that the scale measures one thing and infers the rest. Every item above measures something directly.
Frequently asked questions
How much should I weigh for my height?
Not a single number, but a range. Find your height in the healthy weight range table above. At 170 cm that band runs from 53.5 to 72.0 kg. Where you sit within it depends on your build, muscle mass, and body composition, and any of it can be perfectly healthy.
Which ideal weight formula is the most accurate?
None of them, in the sense you mean. They were built to estimate lean body size for drug dosing, not to define a healthy target. If you want the best-supported answer to "what should I weigh," use the healthy weight range from BMI as your band and your waist-to-height ratio as your check. If you insist on a formula, Devine is the most widely used clinically, but that reflects convention rather than superior accuracy.
Why do the four formulas give me such different answers?
Because they were calibrated near average height and are all linear, while body mass scales closer to the square of height. Near 165 to 175 cm they agree within a couple of kilograms. At 155 cm or 185 cm they can differ by seven or eight. The tables in the disagreement and drift sections above show exactly how much, at each height.
Is BMI accurate?
Accurate at describing populations, unreliable at describing individuals. It was designed for the former by a statistician and adopted for the latter by everyone else. It cannot distinguish muscle from fat, cannot see where fat sits, and does not apply to children, pregnancy, or, arguably, adults over 65. See the BMI Calculator guide for the full breakdown of where it goes wrong.
Is waist-to-height ratio really better than BMI?
For predicting cardiometabolic risk, the evidence says yes, consistently, across multiple meta-analyses. It is also easier to interpret, because the threshold is a sentence rather than a table: keep your waist under half your height. BMI remains useful as a quick population-level screen, and using both is better than either alone.
Does muscle weigh more than fat?
Muscle is denser, so a given volume of muscle weighs more than the same volume of fat. A kilogram of each weighs a kilogram. The practical consequence is that a muscular person occupies less space at the same weight, and BMI counts their muscle as if it were fat.
Does ideal weight change with age?
The formulas do not include age, and the calculator deliberately does not invent an age adjustment, because there is no validated one. What changes with age is the interpretation. Under 18, adult categories do not apply at all. Over 65, the standard thresholds become less reliable and body composition matters more than total mass.
Why does the calculator ask for my sex?
Only because the four historical formulas were published with separate coefficients for male and female bodies. It affects nothing else. Your BMI, your healthy weight range, and your waist ratio are calculated identically regardless of what you select.
Can I be healthy at a weight the table calls overweight?
Yes, and many people are. Fitness, waist ratio, blood pressure, and metabolic markers can all be excellent at a BMI of 27, particularly in muscular people and in older adults. A category on a chart is a prompt to look further, not a diagnosis.
How often should I weigh myself?
Whatever frequency leaves you feeling informed rather than anxious, and if daily weighing makes you anxious, weekly or monthly gives you better information anyway, because it filters out normal fluctuation. Watch the trend across months and ignore the noise between days.
Does the ideal weight differ for men and women?
In the four formulas, yes: the female versions produce lower results at the same height. In BMI, no: the categories are identical. That difference reflects the fact that women typically carry a higher proportion of body fat at the same BMI, which is normal physiology and not a problem to be corrected.
What if I am very tall or very short?
Trust the healthy weight range and treat the four formulas with real scepticism, because their drift is largest at the extremes. The ponderal index, which divides by height cubed, handles the extremes better than BMI and is worth looking at if you are well outside the average range.
Does the calculator store my measurements?
No. Everything is calculated in your browser and nothing is transmitted or saved. Close the tab and it is gone.
When to speak to a professional
A calculator can tell you where a number falls on a chart. It cannot examine you, and it has no idea what else is going on. Some situations genuinely warrant a conversation with a doctor, nurse, or registered dietitian:
- Weight change you did not intend, in either direction, especially if it is rapid
- A waist-to-height ratio of 0.5 or above, or a BMI outside the healthy band, particularly alongside a family history of diabetes or heart disease
- Being under 18, or the parent of someone who is, and wanting growth interpreted properly
- Pregnancy or breastfeeding, where none of the thresholds in this article apply
- Any existing condition, or any medication, that affects weight, appetite, or fluid balance
- Planning a substantial change to how you eat or exercise, which is worth discussing before starting rather than after
And one more, which matters more than any number in this article. If thinking about your weight has started taking up more room in your head than you want it to, if eating has become a source of anxiety, or if you find yourself checking the scale or the mirror in a way that feels compulsive, that is worth telling someone about. It is common, it is treatable, and it is a medical matter rather than a matter of willpower. A doctor is a reasonable first call, and eating disorder helplines exist in most countries for exactly this conversation.
Because a calculator like this one can quietly become a stick to measure yourself against, and no equation written in 1974 to dose an antibiotic deserves that kind of authority over how anyone feels about their body.
The short version
Your ideal weight is a range, not a number. Read it off the healthy weight range table for your height and expect it to be about 18 to 20 kilograms wide, because bodies legitimately differ.
Then get a tape measure and check whether your waist is under half your height. That single check, done properly and repeated consistently, will tell you more about your metabolic health than any of the four formulas ever could, and it costs nothing.
Treat the formulas as what they are: a fascinating piece of medical history, four different answers from four researchers solving four different problems, useful for showing you how uncertain the whole question really is. Which is, in the end, the most honest thing a weight calculator can do. For the deeper dive into BMI itself — its own history, the Asia-Pacific thresholds, and its statistical cousins — the BMI Calculator guide picks up exactly where this one leaves off.
This article is general health information, not medical advice. It cannot account for your medical history, medications, or circumstances. Speak with a doctor or a registered dietitian before making changes to how you eat or exercise, and use any figure here as a starting point for that conversation rather than a conclusion.