The formula
Body mass index is weight divided by height squared. In metric units that is kilograms divided by meters squared; in imperial units it is 703 × pounds divided by inches squared. A person 170 cm tall weighing 65 kg has a BMI of 22.5; someone 5 ft 10 in tall weighing 200 lb has a BMI of 28.7.
Categories
The result is placed in the World Health Organization's adult categories: below 18.5 is underweight, 18.5 to 24.9 is normal weight, 25.0 to 29.9 is overweight, and 30.0 or above is obese. BMI is shown to one decimal place and the category is taken from that same displayed value, so the number and the label you see always agree.
What BMI can and cannot tell you
BMI is a quick screening measure used across populations. It does not measure body fat directly and does not distinguish muscle from fat, so very muscular people can score as overweight. It also does not account for age, sex or ethnicity, and these adult categories are not meant for children or teenagers, who are assessed with age-specific charts. This calculator is not medical advice; talk to a health professional about your own situation.
Privacy
Height and weight are personal health information. They are used only in your browser and are never uploaded or stored.