Body mass index (BMI) is a simple measure that compares body weight with height. It is widely used as a general screening indicator, but it has important limitations. This guide explains the calculation and how to interpret it cautiously.
The BMI formula
BMI = weight in kilograms ÷ (height in metres)²
Example: 70 kg at 1.75 m. Square the height first: 1.75 × 1.75 = 3.0625. Then divide: 70 ÷ 3.0625 ≈ 22.9.
Use the BMI calculator to check your own values.
WHO categories for adults
The World Health Organization classifies adult BMI as follows (see the WHO classification table):
| BMI (kg/m²) | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Normal range |
| 25.0–29.9 | Overweight |
| 30.0 and above | Obesity range |
What BMI does not tell you
- It does not distinguish muscle from fat; athletic people can have a high BMI without excess body fat.
- It does not show where fat is distributed, which can matter for health.
- Children and teenagers are assessed using age-specific percentile charts, not these fixed adult thresholds.
- During pregnancy, in older age and with some health conditions, BMI may be less informative.
Estimate energy needs
If you want to explore daily energy needs, the calorie needs calculator gives a general estimate. It is not a personal recommendation.
This article is for general information and does not replace medical advice. Speak with a qualified health professional about questions related to weight, diet or health.