BMI Calculator
Body mass index from your height and weight
| Weight Status | Min | Max |
|---|---|---|
| Super obese | > 50.0 | |
| Pathologically obese (Class III obesity) | 40.0 | 49.9 |
| Severely obese (Class II obesity) | 35.0 | 39.9 |
| Obese (Class I obesity) | 30.0 | 34.9 |
| Overweight | 25.0 | 29.9 |
| Normal (healthy weight) | 18.5 | 24.9 |
| Underweight | 16.0 | 18.4 |
| Severely underweight | < 16.0 |
How BMI is calculated
BMI (Body Mass Index) is your weight in kilograms divided by the square of your height in metres:
BMI = weight (kg) / height (m)²
Example: a person weighing 70 kg and 1.75 m tall has a BMI of 70 / (1.75 × 1.75) = 22.9. The index does not depend on sex; it was introduced by Adolphe Quetelet in the 19th century, and the weight categories are defined today by the World Health Organization (WHO).
How to interpret the result
The table above shows the weight-status bands used by this calculator. In short, according to the WHO:
| BMI | Weight status |
|---|---|
| < 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| ≥ 30.0 | Obesity |
Important: BMI is a screening indicator, not a diagnosis. It does not measure body composition and thresholds can vary with age and ethnicity. Read it alongside other measures and, if needed, with your doctor.
Why it matters
BMI is the quickest way to gauge weight status at a population level, which is why so many people look it up: it helps estimate the risk linked to overweight and obesity — conditions associated with type 2 diabetes, high blood pressure and cardiovascular disease — as well as flagging underweight.
For a fuller picture, compare it with your ideal weight by the Lorenz formula or the Metropolitan Life tables.
How to measure height and weight
- Weigh yourself in the morning, fasting and after using the bathroom, in light clothing.
- Use a scale on a hard, level surface.
- Measure height barefoot, back straight and gaze horizontal.
- Enter height in centimetres (e.g. 175) and weight in kilograms.
What to do about your result
A BMI in the normal range is a good sign but does not replace an overall assessment. For a value out of range:
- Overweight/obesity: a balanced diet, regular physical activity and, where appropriate, support from a professional.
- Underweight: check possible causes with your doctor and adjust your nutritional intake.
When to see a professional: consult a doctor or dietitian if your BMI is high or very low, if it changes rapidly, or if you have other risk factors. Only a professional can make a clinical assessment.
Limitations of BMI
- It does not distinguish muscle from fat mass: it can overestimate risk in athletes and underestimate it in older adults.
- It does not capture fat distribution (abdominal fat is riskier), which is why a waist measurement is a useful complement.
- It is not suitable for children, pregnant women or some populations without specific adjustments.