Clinical tool
BMI
Body mass index from weight and height, with WHO categories.
Enter weight and height to see the body mass index.
What this calculates
Body mass index: weight in kilograms divided by height in metres squared.
When to use it
As a quick population-level screen for underweight, overweight and obesity, or to document a baseline for adults.
How to interpret it
WHO adult categories: below 18.5 underweight, 18.5 to 24.9 normal weight, 25 to 29.9 overweight, 30 to 34.9 obesity class I, 35 to 39.9 class II, 40 or above class III. Lower action points are suggested for Asian populations.
Important limitations
- BMI does not distinguish fat from muscle, or describe where fat is distributed.
- It can misclassify athletes, older adults with low muscle mass, pregnancy and people of different ethnic backgrounds.
- These adult categories do not apply to children, who need age and sex specific centile charts.
For practising medics only. Clinical tools support judgement, they do not replace it. Always verify results against current guidelines and the patient in front of you.