BMI Calculator

Work out your body mass index from your height and weight, in US or metric units. See your BMI category and the healthy weight range for your height.

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Your BMI
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Healthy range for your height–
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What is BMI?

Body mass index (BMI) is a simple number that compares your weight with your height. Doctors and health organizations use it as a quick first check of whether a person's weight may raise health risks. It is easy to measure, but it is only a starting point, not a measure of body fat or health on its own.

BMI formula

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

For example, someone who is 5 ft 10 in (70 inches) and weighs 170 lb has a BMI of 703 × 170 ÷ 70² ≈ 24.4, which is in the healthy weight range.

Adult BMI categories

BMICategory
Below 18.5Underweight
18.5 to 24.9Healthy weight
25.0 to 29.9Overweight
30.0 and aboveObesity

Limits of BMI

  • It cannot tell muscle from fat, so athletes may show a high BMI.
  • It does not show where fat is stored. Waist size adds useful information.
  • It is not used the same way for children, pregnant people or some older adults.

This calculator is for general information and is not medical advice. Talk to a healthcare professional about your health and weight. To estimate how many calories you burn, try the TDEE calculator.

Last reviewed October 2026.

Frequently asked questions

What is a healthy BMI?

For adults, a BMI from 18.5 to 24.9 is classed as a healthy weight. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or more falls in the obesity range. These are the categories used by the CDC and the World Health Organization.

How is BMI calculated?

BMI is your weight in kilograms divided by your height in meters squared. In US units, it is 703 × weight in pounds ÷ height in inches squared.

Is BMI accurate for everyone?

BMI is a quick screening tool, not a diagnosis. It does not tell muscle from fat, so muscular people can have a high BMI while being healthy. It may also be less accurate for older adults and differs in meaning across some ethnic groups. A doctor can give a fuller picture.

Does BMI work for children and teens?

Not in the same way. For people under 20, BMI is compared with growth charts for their age and sex to give a percentile. This calculator uses the adult categories, so ask a pediatrician about a child's BMI.

Is my information stored?

No. The calculation runs in your browser and nothing you enter is sent or saved.