BMI Calculator

Two measurements are enough, and the result updates as you type. Nothing is stored or uploaded.

1. Set Units to Metric (cm, kg) or Imperial (ft/in, lb).
2. In metric, enter Height (cm). In imperial, use Height: feet (imperial) and Height: inches (imperial), so 5 ft 9 in is entered as 5 and 9.
3. Enter Weight (kg or lb) in whichever unit you chose. Weighing yourself at the same time of day gives more comparable readings, and measuring height without shoes avoids adding a centimetre or two.
4. Read the BMI, the category and the healthy range for your height.

Besides the BMI to one decimal place, the results list your category, the healthy weight range in your chosen units, and how much you would need to gain or lose to reach the nearest edge of that range.

Body mass index divides weight by height squared: BMI = weight (kg) / height (m) squared. For 1.75 m and 70 kg that is 70 / 3.0625, which is 22.9. In imperial mode the tool converts feet, inches and pounds to centimetres and kilograms first, so it matches the familiar 703 x weight (lb) / height (in) squared version: 5 ft 9 in and 160 lb gives 23.6.

The healthy range runs the formula backwards, multiplying the squared height in metres by 18.5 and by 24.9. At 1.75 m that is 56.7 kg to 76.3 kg, or 125.3 lb to 168.6 lb at 5 ft 9 in. The "gain" or "lose" row measures the distance to the nearest edge. Someone of 160 cm weighing 45 kg has a BMI of 17.6, below the lower edge of 47.4 kg, so the tool shows a gain of about 2.4 kg to reach it.

Because height is squared, the healthy range moves quickly with height. These ranges come straight from the 18.5 and 24.9 limits:

A range spanning more than 20 kg for a tall adult is normal, not a fault. Where you sit inside it depends on build, muscle and age. If your height falls between two rows, the formula above gives the exact range, and typing the height into the calculator does the same in one step. Rounding to one decimal place means a BMI such as 24.96 is shown as 25.0 but is still counted in the healthy band, a boundary effect that is too small to matter in practice.

The tool uses the World Health Organization adult bands.

BMI is a screening measure, not a diagnosis. It cannot tell muscle from fat, so a muscular athlete can read as overweight, and it can understate risk in older adults who have lost muscle. Some health services use lower cut-offs for people of South Asian and some other backgrounds, and the adult bands do not apply to children, teenagers or anyone who is pregnant. The result is an estimate for general information and not medical advice.

Because BMI sees only height and weight, it works well beside other numbers. The body fat calculator estimates fat mass from tape measurements, and a waist measurement larger than half your height is linked to higher risk at any BMI. To compare formulas for a target weight, the ideal weight calculator shows four classic estimates, and the calorie calculator estimates daily energy needs. The weight converter and length converter help when your scales or tape use other units.