BMI Calculator (Metric)

Who the BMI Scale Applies To

The WHO categories on this page are for adults aged 18 and over, and they are the same for men and women: sex does not enter the BMI formula and does not move the category boundaries.

Children and teenagers aged 5–19 are read differently. Their BMI is compared with a WHO reference for age and sex and expressed as a z-score (SDS; WHO publishes the same reference as percentile charts): overweight above +1 SD, obesity above +2 SD, thinness below −2 SD and severe thinness below −3 SD. At the top of that range the two scales meet — WHO notes that +1 SD equals a BMI of 25 at 19 years, and +2 SD equals 30. WHO BMI-for-age (5–19 years)

For older adults the WHO classification above draws no separate line by age. Other guidance does, for a different purpose: the ESPEN consensus on diagnosing malnutrition counts a BMI as reduced below 20 under the age of 70 and below 22 above it. On its own that is not a diagnosis: there it only counts alongside mandatory unintentional weight loss. It is a boundary inside a diagnostic criterion, not a healthy weight range, and this page does not apply it. ESPEN Consensus Statement, Clinical Nutrition, 2015