BMI Calculator

How to Use This BMI Calculator

Pick your units, put in your height and weight, and the result updates as you type. US units want feet and inches separately, metric just wants centimetres. Your choice is remembered, so you'll only set it once.

Age and sex are optional, and neither one changes the number. Adult BMI is weight divided by height squared, and that's the whole of it. They're there because they change what the number means: under 20 the adult bands don't apply at all, so the calculator swaps them for a pointer to the right tool rather than showing you a category that was never meant for you.

Beside the result you'll find the weight range that would put your height in the healthy band, which is often the figure people actually came for, and a scale showing where you sit. Take the result away as an image or a PDF if you want it.

The BMI Formula, in Both Unit Systems

The WHO states BMI as weight in kilograms divided by height in metres squared:

BMI = kg ÷ m²

US units need a conversion factor, because pounds and inches aren't kilograms and metres. Multiplying by 703 does the whole conversion in one step:

BMI = 703 × lb ÷ in²

Both give the same answer for the same person, which is worth knowing if you've ever seen two calculators disagree. Height is squared in both, and that's why a small error in your height moves the result more than the same error in your weight.

BMI Example: 5 ft 10 in and 160 lb

Height first, in inches: 5 ft 10 in is 70 inches. Then the US formula.

The same person in metric is 177.8 cm and 72.6 kg, and 72.6 ÷ 1.778² gives 23.0 as well.

What Is a Healthy BMI? The Adult Categories

These are the CDC's bands for adults 20 and older. Each one runs up to, but not including, the start of the next:

Notice the wording: the healthy band ends at "less than 25", not at 24.9. A BMI of exactly 25.0 is overweight. The healthy weight range here is worked out at 18.5 and 24.9, which is what every chart does, so the top of the range sits a fraction under the real boundary. Both ends are rounded inwards rather than to the nearest tenth, so a weight shown in the range is genuinely inside the band, never a hundredth outside it.

BMI Chart: Healthy Weight for Your Height

Most people want the second number more than the first. The healthy band is 18.5 to just under 25 for every adult, but the weights that land in it depend entirely on how tall you are, and height is squared in the formula, so the range climbs fast. Across the table below, two inches of height moves the bottom of the range by about seven pounds and the top by about nine.

Every row here is produced by the calculator above, at the same 18.5 and 24.9, so the chart and the tool cannot drift apart. Put your own height in and you will get the range for it exactly, including the half-inches this table skips. A range is not a target, though. Plenty of healthy people sit outside it, and plenty of people inside it have something worth looking at, which is the whole reason BMI is called a screening measure.

BMI for Men and Women

There is no separate men's or women's version of this, and that is not an oversight. The CDC is explicit: "For adults 20 and older, BMI categories are based on a person's BMI regardless of age, sex, or race." Same formula, same 18.5, same 25, same 30. A man and a woman who are both 5 ft 8 in and 170 lb have the same BMI of 25.8 and land in the same category.

What does differ by sex is the measurement people reach for next. The NIH puts an unhealthy waist circumference at more than 40 inches for men and more than 35 inches for women. Two people can share a BMI and be a long way apart on that, because BMI "does not indicate where in the body that people carry fat", as the CDC puts it. If you want a fuller picture than one number gives, a tape measure around the waist is the cheapest thing to add to it.

One exception matters. Under 20, sex genuinely is part of the calculation: a young person's BMI is compared against others of the same age and sex and reported as a percentile. That is covered below.

How the WHO Classifies Adult BMI

You will see two tables in the wild, and they do not say quite the same thing. The CDC bands above are the ones used in the United States. The World Health Organization works at a global level and publishes fewer lines.

Three things are worth pulling out of that. WHO treats overweight as everything from 25 up, with pre-obesity as the slice below 30, so the same person can be "overweight" and "pre-obese" at once without any contradiction. WHO does not publish the class 1, 2 and 3 split on its public pages; that breakdown is the CDC's, and it is what this calculator shows when your BMI is 30 or more. And WHO names the bands at the edges rather than labelling 18.5 to 25 as healthy, which is a quieter way of making the same point the rest of this page makes: the middle of the range is not a clean bill of health.

Neither body treats these lines as exact. The WHO's own paper calls BMI "a surrogate marker of adiposity", and the numbers are cut-offs for populations before they are anything about you.

BMI Prime and the Ponderal Index

The result card carries two numbers beside your BMI. Neither replaces it and neither is part of the CDC or WHO categories, but each fixes something BMI is bad at.

BMI Prime: how far past the line you are

BMI Prime is your BMI divided by 25, the top of the healthy band. A BMI of 25 gives exactly 1.00. A BMI of 30 gives 1.20, which tells you at a glance that you are twenty per cent above the limit, and 18.5 gives 0.74 whatever your height. The idea comes from a 2006 paper by James Gadzik, who proposed a system that "relates a patient's actual weight to his upper weight limit" on the grounds that a bare BMI "fails to convey a quantitative sense of obesity".

It is useful because 27 and 34 are just numbers, while 1.08 and 1.36 are distances. The catch is that it inherits every weakness BMI has: it is the same measurement, rescaled.

Ponderal Index: weight over height cubed

The Ponderal Index divides weight in kilograms by height in metres cubed rather than squared, and it is reported in kg/m³. The reason it exists is that people are three-dimensional. Square the height and the formula quietly flatters short people and penalises tall ones, which is why a very tall athlete can be pushed into the overweight band by arithmetic alone.

You can see the gap in our own numbers. Someone 155 cm and 60 kg and someone 195 cm and 95 kg both come out at a BMI of 25.0, but their Ponderal Indexes are 16.1 and 12.8. Same index, different builds. The cubed form is the one used for the tri-ponderal mass index in a 2017 JAMA Pediatrics study, which found it estimated body fat better than BMI in adolescents. There are no agreed adult categories for it, which is exactly why it is here as a second opinion and not as a verdict.

What BMI Does Not Tell You

BMI knows two things about you. Everything it misses follows from that.

• It cannot tell muscle from fat. The CDC says it outright: BMI "does not distinguish between fat, muscle, and bone mass". Muscle is denser, so someone who trains hard can sit in the overweight or obesity band carrying very little fat. The WHO calls BMI a surrogate marker of fatness and points to waist circumference as a useful addition.
• It cannot see where fat sits. BMI "does not indicate what types of fat people have", and it cannot show where that fat is carried, which is why the NIH pairs it with a waist measurement.
• It reads the same at every adult age. One set of categories covers everyone 20 and older. Since the number cannot see what the weight is made of, the same BMI at 30 and at 70 does not have to mean the same thing.
• The thresholds are not universal. The NIH notes that health organizations have suggested a lower obesity cut-off, starting at 27.5, for adults with Asian ancestry, because Asian adults have been more likely to develop risks such as high blood pressure and diabetes at lower body weights than white adults.

None of that makes BMI useless. It's quick, it needs no equipment, and across large groups it tracks health outcomes well enough to be worth measuring. It's a starting point for a conversation, not the end of one.

BMI for Children and Teens

Under 20, ignore the adult bands entirely. Children and teens are still growing, so a BMI on its own says very little. The CDC puts it plainly: because they're growing, BMI has to be expressed relative to other children of the same age and sex.

What you get is a percentile rather than a category. A BMI in the 60th percentile means 60% of children that age and sex have a lower one. The CDC's own tool covers ages 2 through 19 and it's the right place for this. Put an age under 20 into the calculator above and it shows the number, drops the adult category, and links you there.

Growth is also why a child's BMI can move a lot in a year without anything being wrong. That's a conversation for a paediatrician, not a calculator.

BMI Calculator FAQ

Sources

The categories and the cautions on this page come from the sources below. The math is ours, and we set out how we do it in the methodology.

• Adult BMI Categories — Centers for Disease Control and Prevention
• Adult BMI Calculator — Centers for Disease Control and Prevention
• Child and Teen BMI Calculator — Centers for Disease Control and Prevention
• About Body Mass Index (BMI) — Centers for Disease Control and Prevention
• Overweight and Obesity: Symptoms and Diagnosis — National Heart, Lung, and Blood Institute, NIH
• Variations exist among Asian American adults with obesity — National Heart, Lung, and Blood Institute, NIH
• WHO discussion paper on obesity (19 August 2021) — World Health Organization
• Gadzik J. "How much should I weigh?" Quetelet's equation, upper weight limits, and BMI prime. Conn Med. 2006;70(2):81-8 — PubMed, National Library of Medicine
• Tri-Ponderal Mass Index vs Body Mass Index in Estimating Body Fat During Adolescence — JAMA Pediatrics, 2017
• Obesity and overweight — World Health Organization

Reviewed by Usman Ali · September 2026