BMI Calculator
Calculate your Body Mass Index (BMI) using metric or imperial units. See your health category and reference ranges.
| Underweight | Under 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese | 30.0 and above |
How It Works
The BMI Calculator computes the Body Mass Index using the standard formula BMI = weight / height², with weight in kilograms and height in metres. Switch between metric (cm, kg) and imperial (feet/inches, pounds) units; the tool applies the correct unit conversions internally and always reports the same dimensionless BMI value, since the index is a ratio. Once you enter both height and weight, the result appears instantly along with a category badge — underweight, normal, overweight, or obese (with class I/II/III sub-ranges) — using the World Health Organization’s adult thresholds (18.5, 25, 30, 35, 40). Underneath the result, the tool shows where you fall on a coloured scale so you can see the distance to neighbouring categories at a glance. The math is unit-aware but otherwise plain arithmetic, performed entirely in your browser; nothing about your height, weight, or category is recorded or transmitted, which is appropriate for a health-related quick reference.
Use Cases
- Getting a quick baseline health metric at home
- Tracking BMI trend over time alongside a diet or exercise programme
- Understanding the WHO classification thresholds
- Comparing BMI between metric and imperial measurements
Frequently Asked Questions
- Is BMI a good measure of health?
- It is a screening tool, not a diagnosis. BMI does not distinguish muscle from fat, so very muscular people can score 'overweight' while being healthy. It is most useful for population statistics and as a starting point.
- Why is the imperial formula different?
- It is the same formula. Pounds and inches are converted to kilograms and metres internally so the resulting BMI is unitless and comparable everywhere.
- What thresholds does the calculator use?
- The WHO adult thresholds: under 18.5 underweight, 18.5–25 normal, 25–30 overweight, 30+ obese (with sub-classes 30–35, 35–40, 40+).
- Is BMI accurate for children or athletes?
- No — different tables apply. For children, paediatric BMI-for-age percentiles are used. Athletes with high muscle mass need body-fat percentage instead.
- Are my numbers sent anywhere?
- No. The calculation runs in your browser; nothing is stored or transmitted.