BMI Calculator
Your BMI, its category, and the healthy weight range for your height.
Runs entirely in your browser
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Weight in kilograms divided by height in metres squared. That is the whole formula, devised by Adolphe Quetelet in the 1830s as a way of describing populations, and it is still the same arithmetic today.
It was never built to assess an individual, and it does not. BMI knows nothing about muscle, bone, body composition or where weight is carried, so a rower and a sedentary person of the same height and weight get the same number and it means opposite things. Sprinters and forwards routinely read as obese. That is not the measure failing at its job; it is the measure being used for a job it was not built for.
The category boundaries are also blunter than they look. They come from observational data in mostly European populations, and the thresholds at which health risk actually rises differ by ancestry: several health bodies use a lower overweight cutoff for people of South Asian descent for exactly this reason.
What the number is genuinely useful for is a rough position and a direction of travel over time. The healthy range shown beside it is the weights that would put this height between 18.5 and 25. None of this is medical advice, and a number on a screen is not a reason to do anything without talking to a doctor.
How to use it
- Enter your weight in kilograms and your height in centimetres.
- Read the number, the category and the healthy range for that height.
- Read the notes below before drawing any conclusion from it.
Questions
How is BMI calculated?
Weight in kilograms divided by the square of height in metres. Someone 175 cm and 70 kg is 70 divided by 1.75 squared, which is 22.9. In pounds and inches the same figure is weight divided by height squared, multiplied by 703, which is the conversion factor rather than anything meaningful.
What are the BMI categories?
Under 18.5 is underweight, 18.5 to 25 healthy, 25 to 30 overweight and 30 or above obese. The boundaries are round numbers drawn across a continuum, so 24.9 and 25.1 are the same person, and several health bodies use a lower overweight threshold for people of South Asian descent.
Is BMI accurate for athletes?
No, and this is its best-known failure. It cannot tell muscle from fat, so a muscular person reads high while carrying very little fat. Sprinters, rowers and forwards routinely land in the obese category. If you train seriously, the number is telling you about your mass and nothing about your health.
What is a healthy weight for my height?
The range shown beside the result is the weights that put your height between 18.5 and 25. Treat it as a wide band rather than a target: it spans a couple of stone for most adults, and where within it anyone should sit is not something a formula from the 1830s can answer.
Is my weight sent anywhere?
No. The calculation happens in this tab and the page is served with a header that forbids it from opening a connection to anywhere. Nothing is stored and nothing is transmitted, which is the least a page asking for your weight can do.
Your data stays on your device
Everything above runs inside your browser as WebAssembly compiled from Rust. Nothing you type is uploaded, logged or stored on a server. You can load this page once, go offline, and it still works.
This page makes no requests at all, to anywhere. That is not a promise in the copy: it is a Content-Security-Policy header your browser enforces, and connect-src on it is none. Open the network tab and watch nothing happen.