BMI Calculator
Work out your body mass index from metric or imperial measurements, see the WHO weight category and the healthy weight range for your height. Nothing you type leaves your browser.
Also available as a desktop app for Windows.
About this tool
Body mass index is one division: weight in kilograms divided by the square of height in metres. A 70 kg adult at 1.75 m lands at 22.9; the same person at 95 kg lands at 31.0. That single number — crude, unit-free and instantly comparable — is why a statistician’s index from the 1830s is still the first line on every intake form a century and a half later.
This tool computes the index and then does the two things the raw number cannot do on its own. First it places the value on the WHO adult scale, which runs from severe thinness below 16.0 through normal weight (18.5–24.9) and overweight (25.0–29.9) to three classes of obesity at 30.0 and above. Second it inverts the formula: for your height, it shows the weight range that corresponds to a BMI of 18.5 to 24.9 — the part people actually act on.
The scale treats 18.5 and 24.9 as boundaries, not targets: within the normal band the health evidence is broadly flat, and the categories themselves say nothing about body composition. That is also why the tool shows its result as a range to sit in rather than a number to hit.
Frequently asked questions
- Is BMI accurate for athletes or older adults?
- Often not. BMI divides weight by height² and stops there — it cannot tell 20 kg of muscle from 20 kg of fat, so muscular people routinely land in the overweight band despite low body fat. In older adults the opposite bias appears: rising frailty shifts composition toward less muscle, so a "normal" BMI can coexist with high fat mass. Waist measurement and body-composition methods exist precisely for these cases; treat BMI as a screening number, not a measurement of you.
- Why does the tool use the WHO categories instead of Asian cutoffs?
- The WHO’s global table is the one this tool displays, because it is the single most widely referenced standard. Some national health authorities use lower overweight thresholds (for example 23.0 and 27.5) after population studies found cardiometabolic risk appearing at lower BMIs in some Asian populations. If your doctor uses those cutoffs, the healthy weight range shown here is not the one to compare against — the formula behind it is the same, only the boundaries move.
- How is the healthy weight range calculated?
- By inverting the same formula: for your height in metres, the range runs from 18.5 × height² to 24.9 × height² in kilograms. At 1.75 m that is 56.7 to 76.3 kg. It is arithmetic, not advice — the range is where the WHO scale places "normal weight", and individual targets should come from a clinician who can see more than two numbers.
- Does it send my numbers anywhere?
- No. The calculation is one division in the page. There is no server, no request and no logging, and the tool keeps working with the network switched off — a practical way to verify the claim yourself.