How it works
Body mass index (BMI) divides weight by height squared. It is a quick screening number used in public health and clinical settings to group adults into broad weight categories.
BMI does not measure body fat directly. Muscular people can have a high BMI with little body fat, and older adults can have a normal BMI while carrying more fat than it suggests. Waist measurements and body-fat estimates add useful context.
The categories shown are the standard adult cut-offs used by the WHO and CDC. Results are estimates for general information, not medical advice.
Formula
BMI = weight (kg) ÷ height (m)² · US units: BMI = 703 × weight (lb) ÷ height (in)²
Questions people ask
What is a healthy BMI for adults?
The WHO and CDC use 18.5 to 24.9 as the "healthy weight" range for adults 20 and older. Below 18.5 is classed as underweight, 25 to 29.9 as overweight and 30 or more as obesity.
Is BMI accurate for athletes?
Often not. BMI cannot tell muscle from fat, so people with a lot of muscle mass may fall in the overweight range while having low body fat. A body-fat or waist-to-height measurement gives a better picture.
Does BMI work for children?
Not with adult cut-offs. For ages 2 to 19, BMI is compared against growth charts for the same age and sex and reported as a percentile.
What is BMI Prime?
BMI Prime is your BMI divided by 25, the upper limit of the healthy range. A value of 1.00 sits at that limit; 0.90 is 10% below it.