About the BMI calculator
Body mass index (BMI) compares your weight with your height in a single number. It is quick to work out and is widely used by doctors and researchers to spot weight ranges that are linked with a higher chance of health problems across large groups of people.
Enter your height and weight in US or metric units. The calculator shows your BMI, the category it falls in, the weight range that matches a BMI of 18.5 to 24.9 for your height, and a scale that marks where you sit. It also reports BMI Prime (your BMI divided by 25) and the ponderal index, an alternative measure that is less sensitive to height.
BMI does not measure body fat directly. Muscular people can score high without carrying extra fat, and older adults or people who have lost muscle can score normal while having a high fat share. For children and teens aged 2 to 19, BMI is read against growth charts for their age and sex rather than the adult categories used here.
BMI categories
For adults the usual bands are: under 18.5 underweight, 18.5 to 24.9 normal weight, 25 to 29.9 overweight, and 30 or more obese. Obesity is often split into Class I (30 to 34.9), Class II (35 to 39.9) and Class III (40 and above). Use the result as a starting point for a conversation with a health professional, not as a diagnosis.
Formula
- BMI = weight (kg) ÷ height (m)²
- US units: BMI = 703 × weight (lb) ÷ height (in)²
- Healthy weight range = 18.5 and 24.9 × height (m)²
- Ponderal index = weight (kg) ÷ height (m)³
Example
A person who is 5 ft 10 in (177.8 cm) tall and weighs 160 lb (72.57 kg) has a BMI of 72.57 ÷ 1.778² = 23.0, which is in the normal weight range. The healthy range for that height is 128.9 lb to 173.5 lb.