BMI calculator (kg and cm, or feet and pounds)
Body mass index from your weight and height, the WHO category it falls in, and the weight range that would put you in the normal band, with the formula shown.
Enter your weight and height.
How BMI is calculated
Body mass index is weight in kilograms divided by height in metres squared:
BMI = weight (kg) ÷ height (m)²
Someone who weighs 70 kg and is 170 cm tall has a BMI of 70 ÷ (1.70 × 1.70) = 70 ÷ 2.89 = 24.2. In pounds and inches the same number is weight × 703 ÷ height², so 154 lb at 5 ft 7 in (67 in) is 154 × 703 ÷ 4,489 = 24.1, the small difference being the rounding of the conversions. The calculator does the unit conversion for you and shows the metric figures it used.
The categories
The World Health Organization's cut-offs for adults, which this page uses, are the same for men and women and do not change with age:
| BMI | WHO category |
|---|---|
| under 17.0 | moderate or severe thinness |
| 17.0 to 18.4 | underweight |
| 18.5 to 24.9 | normal weight |
| 25.0 to 29.9 | overweight (pre-obesity) |
| 30.0 and above | obesity |
The result also shows the weight range that would put you in the normal band at your height, so the number becomes something you can act on: 18.5 to 24.9 at 170 cm is 53.5 kg to 72.0 kg.
What BMI does not tell you
- Where the weight is. WHO's own guidance says the health risk at a given BMI differs between populations, partly because of body proportions, and that in some populations the metabolic consequences of weight gain start at modest levels of overweight. WHO has published separate guidance on lower action points for Asian populations; this page will show that scale beside the standard one once we have read the original document. Until then, a BMI in the upper part of the normal band is not a reason to relax, and waist circumference is the second number a doctor will want.
- Muscle. A wrestler and a sedentary clerk can share a BMI of 27 and be in very different health. BMI was designed for populations, not athletes.
- Children and teenagers. Under 20, BMI is read against age-and-sex growth charts, not these adult cut-offs. This page is for adults.
- Pregnancy. BMI is not used during pregnancy; weight gain targets are set against the pre-pregnancy BMI by the doctor.
- Older adults. Some clinicians accept a slightly higher BMI in people over 65; ask yours.
Measuring properly
Weigh yourself in the morning, after the toilet and before breakfast, in light clothes, on the same scale each time. Measure height without shoes, heels together, standing against a wall with a flat object on the head. A 2 cm error in height moves a BMI of 24 by about 0.6. Track the trend over months rather than the number on one day.