BMI Calculator

Calculate your body mass index in metric or US units, see your weight category and the healthy weight range for your height.

  • Reviewed October 2026
  • Formula and worked example below
  • Free, no sign-up, runs in your browser
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Enter your numbers to see the result.

What BMI measures

Body mass index is a quick screening number that relates your weight to your height. Doctors and public-health agencies use it to sort adults into broad weight categories, because it is easy to measure and correlates reasonably well with body fat across large groups of people.

BMI = weight (kg) ÷ height (m)² BMI = 703 × weight (lb) ÷ height (in)²

Example

A person who weighs 75 kg and is 1.75 m tall has a BMI of 75 ÷ (1.75 × 1.75) = 24.5, which falls in the healthy range. In US units, 165 lb at 5 ft 9 in (69 in) gives 703 × 165 ÷ 4,761 = 24.4.

BMI categories for adults

The World Health Organization and the US Centers for Disease Control and Prevention use the same adult cut-offs: under 18.5 is underweight, 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight and 30 or more is obesity. Obesity is further split into class 1 (30–34.9), class 2 (35–39.9) and class 3 (40 and above). Some Asian health authorities use lower thresholds, such as 23 for overweight, because risk of type 2 diabetes rises at lower BMI in those populations.

Limits of BMI

  • It does not measure fat directly. Muscular athletes can have a high BMI with low body fat.
  • It ignores where fat is stored. Fat around the waist carries more health risk. A waist measurement above half your height is a useful extra warning sign.
  • It differs with age and sex. Older adults tend to have more body fat at the same BMI, and women generally have more body fat than men at the same BMI.
  • It is not for children. Under 20, BMI is compared with age- and sex-specific percentile charts instead of fixed cut-offs.

For a fuller picture, pair BMI with the body fat calculator and talk to a doctor about blood pressure, blood sugar and cholesterol.

Frequently asked questions

What is a healthy BMI?

For most adults, a BMI from 18.5 to 24.9 is considered a healthy weight range.

Is BMI accurate for athletes?

Not very. BMI cannot tell muscle from fat, so muscular people may be classed as overweight even with low body fat. A body fat measurement is more useful for them.

How do I calculate BMI in pounds and inches?

Multiply your weight in pounds by 703, then divide by your height in inches squared. Choose US units above and the calculator does this for you.

Is BMI different for men and women?

The adult formula and categories are the same for both sexes, although women typically have a higher body fat percentage at the same BMI.

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Last reviewed Oct 20, 2026. Results are estimates; check important decisions with a qualified professional.