BMI Calculator
BMI from height and weight, and the band it falls in.
Recent
Formula
How the calculation works
BMI divides weight in kilograms by height in metres squared. The squaring is the part that matters: height is not subtracted, it is multiplied in twice, which is why the same weight reads very differently at 160 and at 190 centimetres.
The number is a screening band, not a measure of health. It cannot see muscle, bone density or where fat sits, so a trained athlete and a sedentary person of the same height and weight get the same figure. Read the band, then read it again beside what you know about your own body.
Common mistakes
- Entering height in metres (1.7) instead of centimetres (170), which makes the BMI about ten thousand times too small.
- Treating the number as a diagnosis. It is a band, and a doctor reads it with other things.
- Using it for a child. Children need age-and-sex growth charts, not the adult bands.
When to use it
- Use it for a quick, rough band on an adult, or to watch a trend over months.
- Do not use it alone to judge health, and not at all for children, pregnant women or athletes.
Worked example
68 kg at 170 cm: a BMI of 23.5, inside the normal band.
Common questions
Is BMI right for everyone?
No. BMI counts weight against height and cannot tell muscle from fat, so a regular athlete can read as overweight while being perfectly healthy. Children, pregnant women and older adults need different charts.
What do the bands mean?
Below 18.5 is under, 18.5-24.9 normal, 25-29.9 over, 30 and above obese. These are population figures, not a personal diagnosis; see a doctor if you are unsure.
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