BMI calculator
Your BMI, its NHS band and the healthy range for your height, in metric or in feet, inches, stones and pounds, with the caveats stated rather than hidden.
Guide
How to use it
- Pick your units. The stones and pounds page starts imperial if that is home for you.
- Enter height and weight; the BMI, band and marker update as you type.
- Read the healthy-weight range for your height beneath the band.
- Then read the caveats, they are part of the answer, not small print.
Examples
Worked examples
75 ÷ 1.75² = 24.5, top end of the healthy band. The healthy range for that height runs roughly 57 to 76 kg.
Converted exactly (1.626 m, 72.6 kg), BMI is 27.5, in the overweight band, with a healthy range of about 7 st 11 to 10 st 6 for that height.
1.85 m and 102 kg of mostly muscle reads 29.8, nearly obese on paper. This is the textbook case for pairing BMI with a waist measurement.
Method
How it works, and what it cannot tell you
BMI is weight in kilograms divided by height in metres squared, a 19th-century population statistic that survives because it is simple and roughly tracks body fat across large groups. Imperial entries are converted with exact factors before the same formula, so both unit systems give identical results.
What it cannot do: distinguish muscle from fat, see where fat sits (waist matters more than thighs), or apply to children, pregnancy and frail older adults. NHS guidance also lowers the action thresholds to 23 and 27.5 for several ethnic groups. Treat the number as a conversation starter with a GP, not a verdict, and note nothing you enter here is stored or sent anywhere.
FAQ
Frequently asked questions
How is BMI calculated?
Weight in kilograms divided by height in metres squared. 75 kg at 1.75 m is 75 ÷ 3.06 = 24.5. Imperial inputs are converted exactly before the same formula.
What are the NHS BMI categories?
Under 18.5 underweight, 18.5 to 24.9 healthy, 25 to 29.9 overweight, 30 to 39.9 obese, 40 and over severely obese, for most adults.
Why does muscle skew BMI?
BMI only knows mass, not what it is made of. Muscle is denser than fat, so rugby players and lifters read overweight while carrying little fat. Waist measurement is the usual companion check.
Does ethnicity change the thresholds?
NHS guidance applies lower action thresholds (23 for increased risk, 27.5 for high risk) for people of Asian, Black African and some other backgrounds, because health risks rise at lower BMIs.
Does BMI apply to everyone?
No. It is not designed for under-18s (they use centile charts), pregnancy, or frail older adults. For most other adults it is a reasonable first screen, no more. The for women page covers the sex question honestly.
Is my data stored?
No. The calculation happens in your browser; height and weight are never transmitted or saved.
More tools