How BMI is calculated
BMI = weight (kg) ÷ height (m)2
In imperial units the formula is 703 × weight (lb) ÷ height (in)².
The standard categories
| BMI | Category |
|---|---|
| Below 16 | Severely underweight |
| 16 – 18.4 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25 – 29.9 | Overweight |
| 30 and above | Obese |
What BMI is good for — and what it is not
BMI is a population screening tool, not a diagnosis. It was designed for statistical use across large groups, and it has well-known blind spots:
- Muscle weighs more than fat. A trained athlete can score "overweight" while carrying very little fat.
- It ignores fat distribution. Fat around the abdomen carries different risks from fat on the hips, and BMI cannot tell them apart.
- It ignores age and sex. The same number means different things at 20 and at 70.
- Ethnic thresholds differ. Some health bodies use a lower overweight threshold (23) for people of South Asian descent.
A more complete picture comes from combining BMI with waist circumference, body-composition measurements and your own medical history. Talk to a clinician before drawing conclusions from any single number.
This tool is for general information only and is not medical advice.