BMI
Body mass index
Estimate, not medical advice.
Work out a body mass index from a weight and a height, in metric or imperial units. BMI places a build within the ranges defined by the World Health Organization.
How it works
The index relates weight to the square of height. That square means BMI does not vary proportionally with stature, which explains part of its limitations at extreme heights.
BMI = weight (kg) ÷ height (m)²
Frequently asked questions
How do I read the result?
Below 18.5 the WHO speaks of underweight, 18.5 to 25 of a normal build, 25 to 30 of overweight, and above 30 of obesity. Those thresholds apply to adults.
Is BMI reliable?
It is a population indicator, not a diagnosis. It does not tell muscle from fat and says nothing about how either is distributed: a very muscular athlete regularly falls outside the range with no health issue whatsoever.
Does it apply to children?
Not with these thresholds. For children and teenagers, BMI is read against growth charts by age and sex, not against fixed values.