BMI Calculator
Work out body mass index from height and weight, in metric or imperial units, with the healthy weight range for your height.
The formula
In metric units, BMI is weight in kilograms divided by height in metres squared:
BMI = kg ÷ m²
In imperial units the same ratio needs a conversion constant:
BMI = 703 × lb ÷ in²
Worked example
Someone 175 cm tall weighing 70 kg:
m = 175 ÷ 100 = 1.75m² = 3.0625BMI = 70 ÷ 3.0625 = 22.9
That falls in the healthy range.
The categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obese |
These are the World Health Organization’s cut-offs for adults.
What BMI cannot tell you
BMI is a ratio of weight to height and nothing more. It does not distinguish muscle from fat, so a muscular athlete is routinely classed as overweight by it. It does not account for where fat is carried, which matters more for cardiovascular risk than the total. It was designed to describe populations, not to assess individuals, and the healthy-range boundaries differ for some ancestries. Several health bodies use a lower overweight threshold for people of South Asian descent.
Treat the number as one rough screening signal. It is not a diagnosis, and it is not a substitute for talking to a doctor.