BMI Calculator
Work out body mass index from weight in kilograms and height in centimetres, and see which of the World Health Organization's adult categories the result falls into. BMI is a rough screening measure rather than a diagnosis, and it is worth understanding what it does and does not tell you.
BMI is a rough screening number, not a medical assessment. It can't tell muscle from fat — athletes often score “overweight” while being perfectly healthy — and the standard adult ranges don't apply to children, pregnant women or the elderly. For anything health-related, talk to a doctor; this tool is informational only.
How to calculate your BMI
- Enter your weight in kilograms.
- Enter your height in centimetres.
- Read your BMI and where it falls on the WHO adult scale.
When you'd use this
- A general health check — A quick starting point for a conversation with a doctor.
- Tracking a change — Following the direction of a figure over months rather than fixating on one reading.
- Forms that ask for BMI — Some insurance, fitness and medical forms request it directly.
- Understanding a category — Seeing where a number sits on the standard scale.
Good to know
- It is a screening tool, not a diagnosis — BMI says nothing about body composition, fitness, or health on its own. A doctor interprets it alongside far more information.
- Muscle weighs more than fat — Athletic and muscular people frequently land in the overweight band despite very low body fat. The formula cannot tell muscle from fat.
- The adult scale does not fit everyone — The WHO categories are for adults. Children, pregnant women and older adults are assessed against different references.
- Metric units only — Enter weight in kilograms and height in centimetres. Values outside a plausible human range are rejected rather than producing a nonsense figure.
Frequently asked questions
What formula does this use?
The standard one used worldwide: BMI = weight in kilograms ÷ (height in metres)². A 68 kg person who is 1.70 m tall has a BMI of 23.5.
What are the WHO adult ranges?
Under 18.5 is classed as underweight, 18.5–24.9 normal, 25–29.9 overweight, and 30 or above obese. These are population-level screening bands, not a diagnosis for any individual.
Why isn't BMI enough on its own?
It only relates weight to height — it can't see body composition. Muscular people score high without excess fat, and it says nothing about where fat is carried, which matters medically. A doctor looks at much more than this one number.
What are the BMI categories?
On the WHO adult scale: below 18.5 is underweight, 18.5 to 24.9 is the normal range, 25 to 29.9 is overweight, and 30 or above is obese.
Is BMI accurate for everyone?
No, and it is important to say so. It does not distinguish muscle from fat, ignores where weight is carried, and was never designed to assess an individual. Athletes, older adults and children are all poorly served by it.
How do I convert my height and weight to metric?
One foot is 30.48 centimetres and one pound is about 0.4536 kilograms. The Unit Converter will do both conversions for you.