BMI Calculator

Calculate adult body mass index using US or metric units and see the standard BMI screening category.

YOUR BMI
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—
UnderweightBelow 18.5
Healthy weight18.5–24.9
Overweight25.0–29.9
Obesity30.0 or higher
What this means: BMI is a screening measure based on height and weight. It does not directly measure body fat or diagnose health. Muscle mass, age, sex, body composition, pregnancy, and other factors can affect how BMI should be interpreted. The adult categories shown here are not intended for children or teens.
For informational purposes only. This tool is not medical advice and should not be used to diagnose a health condition. If you have questions about weight or health risk, consider discussing them with a qualified healthcare professional.

How to use the BMI calculator

Choose US units (feet, inches, and pounds) or Metric (centimeters and kilograms), enter your height and weight, and press Calculate BMI. You will see your body mass index and the standard adult category it falls into.

How BMI is calculated

Body mass index compares your weight with your height:

  • Metric: BMI = weight in kilograms ÷ (height in meters)²
  • US units: BMI = 703 × weight in pounds ÷ (height in inches)²

Example (US): someone 5 feet 9 inches tall (69 inches) who weighs 160 pounds has a BMI of 703 × 160 ÷ (69 × 69) = 23.6.

Example (metric): someone 175 cm tall who weighs 70 kg has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.

Standard BMI categories for adults

These are the ranges used by the World Health Organization and the US Centers for Disease Control and Prevention for adults aged 20 and older:

  • Below 18.5 – underweight
  • 18.5 to 24.9 – healthy weight
  • 25.0 to 29.9 – overweight
  • 30.0 and above – obesity

What BMI can and can’t tell you

BMI is popular because it is quick, free, and needs only two measurements. It is a useful screening number for large groups of people, but it is not a diagnosis and it doesn’t measure body fat directly. Keep these limits in mind:

  • Muscle weighs more than fat. Athletes and very muscular people can have a “high” BMI while being very fit.
  • Age matters. Older adults often have less muscle, so the same BMI can mean more body fat.
  • Where you carry weight matters. Fat around the waist is linked to higher health risks than fat elsewhere, and BMI can’t see the difference. Waist measurement is a useful second check.
  • Ethnic background. Some health organizations use lower cut-off points for people of Asian descent, because health risks can rise at a lower BMI.
  • Children and teens need age- and sex-specific BMI percentiles, so this adult calculator is not suitable for them.

If your result surprises you or concerns you, a doctor can look at the full picture, including blood pressure, blood tests, and family history.

Common questions

Is a BMI of 25 bad?

Not necessarily. 25 is simply where the “overweight” range begins. Health depends on many factors, and BMI is only a starting point for a conversation.

Why does the US formula use 703?

It converts pounds and inches into the metric units the original formula was designed for, so both versions give the same answer.

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