BMI only needs a scale and a tape measure, which is why it is used to compare weight across millions of people. But it is a blunt tool when it comes to one person.
What BMI can’t see
BMI cannot tell fat from muscle and bone, and it doesn’t show what type of fat someone has or where it sits in the body.
“BMI does not distinguish between fat, muscle, and bone mass.”
Screening, not diagnosis
BMI is a quick screening measure of weight relative to height — for an individual it should be considered alongside medical history, habits, a physical exam and lab tests.
“BMI is a quick, safe, and reliable screening measure to assess a person's weight relative to their height.”
Why it is still used for statistics
Because BMI is simple and measured the same way everywhere, it allows fair comparisons between countries and over decades. That is exactly what this site uses it for — describing populations, not judging individuals.
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Written by the ObesitySurvey team. Not medical advice.