How to use the BMI Calculator
- Choose feet and pounds or centimetres and kilograms.
- Enter your height and weight.
- Read your BMI, its category and the healthy weight range for your height.
How it works
BMI divides your weight by the square of your height. It is a quick screening number used by doctors and public health bodies, but it does not measure body fat directly. Very muscular people can have a high BMI without excess fat, and BMI says nothing about where fat is stored.
The categories below are the World Health Organization's adult cut-offs. Some guidelines use lower cut-offs for people of South Asian, Chinese and other Asian backgrounds. Children and teenagers use age- and sex-specific percentiles instead, so this calculator is for adults aged 18 and over.
Formula
BMI = weight (kg) ÷ height (m)² BMI = 703 × weight (lb) ÷ height (in)²
Example
Someone 5 ft 9 in tall weighing 165 lb has a BMI of 24.4. In metric, 175 cm and 72 kg gives 23.5. Both fall in the healthy weight range.
Adult BMI categories (WHO)
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
BMI and waist size
Health services often pair BMI with waist measurement, because fat around the middle carries more health risk. Measure around your waist halfway between your lowest rib and the top of your hip bone. As a general guide used by several health bodies, a waist of more than 40 inches (102 cm) in men or 35 inches (88 cm) in women points to higher risk, whatever the BMI.
If your BMI is outside the healthy range, it is a reason to talk to a doctor rather than a diagnosis. They can look at blood pressure, blood tests, family history and fitness alongside your weight.
Frequently asked questions
What is a healthy BMI?
For adults, 18.5 to 24.9 is the healthy weight range in the WHO classification.
Is BMI accurate for athletes?
Not very. Muscle is dense, so muscular people often score as overweight. Waist measurement or body-fat tests give a better picture.
Is BMI different for men and women?
The adult formula and categories are the same for both. Body fat at the same BMI tends to differ between men and women, which is one of the measure's limits.
Can children use this calculator?
No. Children and teens need BMI-for-age percentiles from a pediatric chart.
Last reviewed October 20, 2026. Spotted an error? Tell us.