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.
Worked Example
A person weighing 70 kg at 1.75 m tall: BMI = 70 ÷ 1.75² = 22.9, which lands in the healthy range (18.5–25) — the category cards highlight exactly where the value falls. Switch to imperial and 154 lb at 5’9” gives the same 22.7–22.9 result, since the tool converts internally rather than using the rougher ×703 shortcut tables. The scale visualisation shows how far the value sits from each category boundary, which is more informative than the single number alone.
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.