Updated July 8, 2026
BMI categories reference
Body Mass Index sorts adults into categories by weight relative to height. This sheet lists the WHO ranges and the formula. BMI is a population screen, not a diagnosis.
WHO adult categories
| BMI range | Category |
|---|---|
< 16.0 | Severe thinness |
16.0 - 16.9 | Moderate thinness |
17.0 - 18.4 | Mild thinness |
18.5 - 24.9 | Normal range |
25.0 - 29.9 | Overweight (pre-obese) |
30.0 - 34.9 | Obese class I |
35.0 - 39.9 | Obese class II |
>= 40.0 | Obese class III |
Formula
Metric: BMI = weight(kg) / height(m)^2
Imperial: BMI = 703 * weight(lb) / height(in)^2A screen, not a diagnosisBMI ignores muscle vs fat, age, sex, and body composition, so it misclassifies athletes and others. Use it as a rough screen; consult a clinician for health decisions.
Different rules for childrenFor children and teenagers, BMI is compared against age-and-sex percentile charts rather than these fixed adult ranges.
References
Questions
What is a normal BMI range?
For most adults, 18.5 to 24.9 is the normal range under the WHO classification. Below 18.5 is underweight and 25 or above moves through overweight and obese categories.
What BMI is considered obese?
A BMI of 30.0 or higher is classed as obese, split into class I (30-34.9), class II (35-39.9), and class III (40 and above).