How this calculator works
Adults use fixed BMI screening boundaries, while children use age- and sex-specific CDC 2000 LMS reference data. The child mode uses the same published data as our child BMI page. Inverse adult modes give measurements corresponding to an entered BMI; they do not recommend a target. Pregnancy, muscle mass and fluid retention affect interpretation. The result is an estimate for information only and is not medical advice.
Formula
BMI = weight(kg)/height(m)². Adult overweight begins at 25 and obesity at 30. In children, overweight is the 85th to below the 95th BMI-for-age percentile, and obesity begins at the 95th.
Worked example
An adult 1.80 m tall and 81 kg has BMI 25.0, at the overweight boundary. At 1.80 m and 97.2 kg, BMI is 30.0, at the obesity boundary.
Advertisement
Frequently asked questions
Why does a child need age and sex?
BMI changes with growth. The CDC reference compares a child with the appropriate age and chart-sex group.
Is the weight result a prescription?
No. It is only the weight that satisfies the entered mathematical BMI value.
Can muscular adults be misclassified?
Yes. BMI cannot distinguish muscle from fat, so a clinical assessment considers more than this index.