Quick start
- Choose metric or imperial units.
- Metric: enter weight in kg and height in cm. Imperial: enter weight in lb, feet in the height box and the extra inches in the last box.
- Read your BMI, the category and the healthy weight range.
The formula
BMI = weight in kilograms ÷ (height in metres)². For 70 kg and 175 cm: 70 ÷ 1.75² = 70 ÷ 3.0625 ≈ 22.9.
In imperial units the formula is BMI = 703 × weight in pounds ÷ (height in inches)². For 160 lb at 5 ft 9 in (69 inches): 703 × 160 ÷ 4,761 ≈ 23.6.
BMI categories for adults
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25 to 29.9 | Overweight |
| 30 to 34.9 | Obesity class I |
| 35 to 39.9 | Obesity class II |
| 40 and above | Obesity class III |
These are the World Health Organization ranges for adults. Some health services use lower cut-offs for people of South Asian, Chinese and other Asian backgrounds.
What BMI does not tell you
BMI is a quick screening number based only on height and weight. It cannot tell muscle from fat, so athletes may score high, and it does not show where fat is stored. It is not designed for children, teenagers or pregnant women. Use it as a starting point and speak to a doctor about your own health.
Common questions
What is a healthy BMI?
For most adults, a BMI from 18.5 to 24.9 is considered healthy.
How do I enter 5 feet 9 inches?
Choose imperial, type 5 in the height box and 9 in the extra inches box.
Can children use this calculator?
No. Children and teenagers are assessed with BMI-for-age charts, which compare them with others of the same age and sex.
Is BMI a diagnosis?
No. It is a screening tool. A doctor will look at other measures before drawing any conclusion about health.