What Is Body Mass Index (BMI)?
Definition
Body Mass Index (BMI): Weight in kilograms divided by the square of height in metres. The World Health Organization treats 18.5–24.9 as the normal range for adults.
Body mass index (BMI) is your weight in kilograms divided by the square of your height in metres, in kg/m². The World Health Organization (WHO) classes adults by it: below 18.5 underweight, 18.5–24.9 normal, 25.0–29.9 overweight, 30.0 or more obesity. BMI does not tell muscle from fat. This page is general information, not medical advice.
Where it appears in the formulas
BMI = weight (kg) / height (m)². The BMI calculator rounds the result to one decimal and gives the WHO category for that value. Turned around, the same formula gives the healthy weight range for a height: from 18.5 × height² to 24.9 × height². The ideal weight calculator shows this range too.
Who it does not apply to
The categories are for adults of 18 or older. Children and teens use percentiles by age and sex, and BMI is not interpreted in pregnancy. A muscular person can have a high BMI with little body fat.