How to calculate your BMI
- Choose Metric (kilograms and centimeters) or Imperial (pounds, feet and inches).
- Enter your weight. In imperial, enter height as feet plus extra inches.
- Read your BMI, the category, and the healthy weight range for your height.
BMI is a rough screening measure. It is a starting point for a conversation, not a diagnosis. Talk to a doctor about your health.
The formula
Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = 703 × weight (lb) ÷ height (in)²
The tool converts imperial values to metric exactly (1 lb = 0.45359237 kg and 1 in = 2.54 cm), so both systems agree.
Worked example
A person weighs 70 kg and is 175 cm tall.
- Height in meters: 1.75, and 1.75² = 3.0625.
- BMI = 70 ÷ 3.0625 = 22.9, which falls in the normal range.
- Healthy range for this height: 18.5 × 3.0625 = 56.7 kg up to 24.9 × 3.0625 = 76.3 kg.
The same person in imperial units is 154 lb and 5 ft 9 in (69 inches): 703 × 154 ÷ 69² = 22.7. The small gap comes from rounding 175 cm to 5 ft 9 in.
BMI ranges (adults)
| BMI | Category |
|---|---|
| below 18.5 | Underweight |
| 18.5 to 24.9 | Normal weight |
| 25 to 29.9 | Overweight |
| 30 and above | Obese |
Some groups, including many South Asian populations, face higher health risks at lower BMI values, so local guidelines can use tighter cut-offs.
What BMI cannot tell you
- Muscle is denser than fat, so athletes can score as overweight.
- It ignores waist size, age, sex and family history.
- It is not designed for children, teenagers or pregnancy. Growth charts exist for those.
Related tools
Change units with the kg to lbs converter or the cm to inches converter, or browse the weight converter. For a change in weight over time, use the percentage calculator. Your numbers stay on your device.