BMI Calculator
Your BMI, the band it falls in, and — more usefully — the actual weight range that band corresponds to at your height. Nothing is sent anywhere.
Runs on your device — your measurements are never sent anywhereRisk rises at a lower BMI in South and East Asian populations, so many national guidelines set overweight at 23 rather than 25.
BMI is weight divided by height squared. It cannot tell muscle from fat, does not know where the weight sits, and was never designed to describe an individual. It is a screening number, not a diagnosis.
How it works
No account, and your height and weight never leave your computer.
Choose your units
Centimetres and kilograms, or feet, inches and pounds. The imperial answer also gives the weight in stones.
Put in your height and weight
The answer updates as you type. Nothing is stored and nothing is transmitted.
Read the range, not just the number
The useful part is the weight range that matches a healthy BMI at your height — a span of several kilograms, not a single target.
What BMI is actually for
A first look at whether weight is worth discussing
That is the job it does well: flagging, at a glance, whether a conversation with a doctor is worth having.
Forms and screenings that ask for it
Insurance applications, some surgical assessments and occupational health checks all ask, whatever its limitations.
Seeing what a healthy range looks like at your height
More useful than the number itself, because it is a range of several kilograms rather than a single figure to hit.
Tracking a direction over time
The trend across months says more than any single reading, and needs no equipment beyond scales.
What BMI measures, and what it does not
Body mass index is your weight in kilograms divided by your height in metres squared. That is the entire calculation. It was devised in the 1830s by Adolphe Quetelet, a Belgian statistician, who was describing populations and said explicitly that it was not for assessing individuals.
It survived because it needs nothing but scales and a tape measure, and because across a large group it correlates reasonably well with body fat. Both of those are still true. Neither makes it a good description of any particular person.
The bands
| BMI | Standard (WHO) | Asian cut-offs |
|---|---|---|
| Under 18.5 | Underweight | Underweight |
| 18.5 – 24.9 | Healthy weight | Healthy to 22.9 |
| 23 – 27.4 | — | Increased risk |
| 25 – 29.9 | Overweight | — |
| 30 and over | Obese | High risk from 27.5 |
The second column is not a curiosity. Risk of type 2 diabetes and cardiovascular disease rises at a lower BMI in people of South and East Asian descent, and the WHO acknowledged this in 2004. India, China, Japan, Singapore and others use the lower thresholds in national guidance. Using the standard bands for those populations understates risk, which is why both are offered here.
Where it is simply wrong
Muscle weighs more than fat. BMI cannot tell them apart, so a rugby player, a sprinter and most people who lift weights seriously will land in "overweight" or "obese" while carrying very little fat. This is the criticism everybody knows, and it is correct.
It ignores where the weight is. Fat around the abdomen carries far more metabolic risk than fat on the hips and thighs. Two people with identical BMIs can have quite different risk profiles, and waist measurement captures some of what BMI misses — a waist over half your height is a rough and useful second check.
It is unreliable at the extremes of height. The formula divides by height squared, but bodies do not scale that way. Very tall people are pushed up the scale and very short people down, for no physiological reason.
It says nothing about age or composition. Muscle is lost with age while fat is gained, so an older person can have an unchanged BMI and a substantially different body.
Who it does not apply to at all
These bands are for adults who are not pregnant.
Children and teenagers are assessed against age and sex percentile charts, because a growing body's normal ratio changes month by month. An adult BMI number for a twelve-year-old is meaningless.
During pregnancy the number stops describing anything useful; pre-pregnancy BMI is what clinicians use.
Athletes and anyone with substantial muscle mass will read high, and the reading should be disregarded rather than explained.
So what is it good for
Two things, and it does both well.
As a population screen it is excellent — cheap, consistent, and good enough across thousands of people to spot trends and allocate health resources. That is what Quetelet built it for.
As a personal flag it is a reasonable prompt. A BMI well outside the healthy band is a decent reason to talk to a doctor, who will then look at the things BMI cannot see: waist, blood pressure, blood sugar, cholesterol, family history and what you actually do all day.
What it is not is a verdict. A number in the healthy band does not mean healthy, and a number outside it does not mean unhealthy. It means one ratio, of two measurements, sits where it sits.
Why the range matters more than the number
A healthy BMI is a band roughly six points wide, which at average height is around twenty kilograms of range. That is deliberate — there is no single correct weight for a height, and treating one number as a target is the least useful way to read this calculator.
The range shown with your result is that band converted back into weight at your height. It is the part worth writing down.
This page does arithmetic and nothing more. It is not medical advice, and nothing here replaces a conversation with a doctor who can see the rest of the picture.
Common questions
How is BMI calculated?
Weight in kilograms divided by height in metres squared. In imperial units it is weight in pounds divided by height in inches squared, multiplied by 703 — which is the same sum with the conversion folded in. The working is shown with your result.
What is a healthy BMI?
18.5 to 24.9 on the standard WHO bands, or 18.5 to 22.9 on the lower cut-offs used across much of Asia. That is a range of about twenty kilograms at average height, not a single target.
Why are there different bands for Asian populations?
Because risk of type 2 diabetes and heart disease rises at a lower BMI in people of South and East Asian descent. The WHO recognised this in 2004 and several countries set overweight at 23 rather than 25 in national guidance.
Is BMI accurate for muscular people?
No. It cannot tell muscle from fat, so athletes and anyone who lifts seriously will often read as overweight or obese with very little body fat. In that case the number should be disregarded rather than explained away.
Does BMI work for children?
Not these bands. Children and teenagers are assessed on age and sex percentile charts, because the normal ratio of weight to height changes as a body grows.
Should I use BMI or waist measurement?
Both, if you are checking. BMI misses where the weight sits, and abdominal fat carries more risk than fat elsewhere. A waist under half your height is a useful second check that BMI cannot give you.
Are my measurements sent anywhere?
No. The arithmetic happens in your browser and nothing is transmitted, stored or logged. There is no server involved.
Is BMI a diagnosis?
No. It is one ratio of two measurements, useful as a prompt to look further. What matters is what a doctor can see that BMI cannot: waist, blood pressure, blood sugar, cholesterol and family history.
More tools
Every one of them runs on your device. No uploads, no accounts.