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BMI Calculator

Calculate your body mass index in metric or imperial units.

Units
cm
kg

BMI is designed for adults aged 20 and over. For children and teens, doctors use age- and sex-specific growth charts.

Enter your height and weight

Your BMI appears here instantly.

Results are estimates for general information only and are not medical advice. Talk to a doctor or other qualified health professional about your health. Read our disclaimer.

When to use it

Body Mass Index (BMI) is a quick screening number that compares your weight to your height. Doctors, insurers and fitness programs use it as a first check of whether weight may be affecting health. Use this calculator to see your BMI, which category it falls in, and the healthy weight range for your height. It’s a starting point for a conversation with a health professional, not a diagnosis.

How to calculate your BMI

  1. Choose Units: Metric (cm, kg) or US (ft, lb).
  2. Enter your Height (in cm, or feet and inches).
  3. Enter your Weight (in kg or pounds).
  4. Your BMI appears instantly under Your BMI, with a colored scale from 15 to 40 and your category.
  5. Check Healthy weight for your height to see the weight range that gives a BMI of 18.5 to 24.9.

BMI is designed for adults aged 20 and over.

A worked example

Alex is 170 cm tall and weighs 65 kg. BMI is weight divided by height in meters squared: 65 ÷ (1.70 × 1.70) = 65 ÷ 2.89 = 22.5, which is in the healthy range. The healthy weight range for 170 cm is about 53.5 to 72 kg. In US units, someone 5 ft 7 in tall weighing 150 lb has a BMI of about 23.5.

What the categories mean

  • Under 18.5 (underweight): may point to undernutrition or another health issue.
  • 18.5 to 24.9 (healthy weight): the range linked with the lowest risk for most adults.
  • 25 to 29.9 (overweight): a higher risk of conditions like type 2 diabetes and high blood pressure.
  • 30 and above (obesity): the risk rises further as BMI goes up.

Limits of BMI

  • It doesn’t measure body fat directly, so very muscular people can score high.
  • It ignores where fat is stored. Fat around the waist carries more health risk; a waist over about half your height is a useful warning sign.
  • It’s less reliable during pregnancy, for older adults and for some ethnic groups.

Tips and common mistakes

  • Measure height without shoes and weigh yourself at the same time of day, ideally in the morning.
  • Don’t mix units: choose US units for feet and pounds rather than converting by hand.
  • Track the trend, not one reading. Weight changes by a kilo or two during the day.
  • Don’t use adult categories for children.

Estimate body fat with the Body Fat Calculator, find your daily energy needs with the Calorie Calculator, or check how much to drink with the Water Intake Calculator.

Frequently asked questions

What is a healthy BMI?

For most adults, a BMI from 18.5 to 24.9 is considered healthy. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or more is in the obesity range. These are the World Health Organization's adult categories.

Is BMI accurate for athletes and older people?

Not always. BMI can't tell muscle from fat, so muscular people may show as overweight while being very fit. Older adults may have a "healthy" BMI but little muscle. Waist size or a body fat estimate gives extra context.

Can children use this calculator?

No. For people under 20, doctors compare BMI with growth charts for the same age and sex. The adult categories here don't apply to children and teenagers.

Do the categories differ for different ethnic groups?

Some health bodies use lower thresholds for people of South Asian, Chinese and some other backgrounds, because health risks start at a lower BMI. Ask your doctor which applies to you.

Is my information saved?

No. Your height and weight are used only in your browser to calculate the result.

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