What BMI measures
Body mass index is weight in kilograms divided by height in metres squared. Adult BMI categories are commonly used to describe weight status at a broad screening level.
What BMI does not measure
BMI does not directly measure body fat, muscle mass, bone density, fat distribution, pregnancy status or individual health. Athletes, older adults and people with different body composition can be misclassified.
Children and teens
Adult BMI categories should not be treated as child or teen BMI categories. Pediatric assessment normally uses age- and sex-specific percentiles.
Practical use
Use BMI as a rough screening number, then interpret it alongside clinical context, waist measures, health history and professional advice where relevant.
References
Last reviewed: 2026-05-13