BMI Calculator: Body Mass Index for Adults
This BMI calculator works out your body mass index from your height and weight, in metric (cm and kg) or US units (feet, inches and pounds). It shows your BMI category using the standard adult ranges from the World Health Organization and the CDC, plus the weight range considered healthy for your height. BMI is a quick screening number, not a diagnosis.
Calculated in your browser. Your height and weight are not sent to or stored on our server. This tool is for adults aged 20 and over and is not medical advice.
Quick answer: BMI = weight in kilograms ÷ (height in metres)². For someone 170 cm tall weighing 68 kg: 68 ÷ (1.70 × 1.70) = 23.5, which is in the healthy range of 18.5 to 24.9. In US units, BMI = 703 × weight in pounds ÷ (height in inches)².
BMI chart for adults
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25.0 to 29.9 | Overweight |
| 30.0 to 34.9 | Obesity class 1 |
| 35.0 to 39.9 | Obesity class 2 |
| 40 and above | Obesity class 3 (severe obesity) |
These are the adult categories used by the World Health Organization and the US CDC. They apply to adults aged 20 and over, for both men and women.
How to use the BMI calculator
- Choose metric or US units. Switching converts the values you entered.
- Enter your height and weight. The BMI, category and marker on the color scale update as you type.
- Healthy weight for your height shows the weight range that gives a BMI of 18.5 to 24.9.
- BMI Prime is your BMI divided by 25, the upper healthy limit; values above 1.0 are above the healthy range.
Limits of BMI
BMI is a simple screening tool based only on height and weight. It doesn’t measure body fat directly or show where fat is stored, so it can be misleading for some people:
- Muscular people and athletes can have a high BMI with little body fat.
- Older adults may have a normal BMI but less muscle and more fat.
- Ethnicity: health risks can start at lower BMIs in people of South Asian, Chinese and some other Asian backgrounds. The WHO has suggested lower action points for Asian populations, and UK guidance (NICE) uses 23 and 27.5 as thresholds for overweight and obesity in these groups.
- Pregnancy: BMI isn’t used to assess weight during pregnancy.
- Children and teens need BMI-for-age percentiles, which compare them with others of the same age and sex. Use the CDC’s child and teen BMI calculator instead.
Waist size adds useful information: a waist over about 102 cm (40 in) for men or 88 cm (35 in) for women is linked to higher health risks. For a full picture, talk to a doctor, who can consider blood pressure, blood tests and family history.
Track progress with our percentage calculator, or time workouts with the stopwatch and timer.
FAQ
Is BMI different for men and women?
For adults, the same BMI ranges apply to both. Body fat at a given BMI usually differs, though.
Is my data saved?
No. The calculation happens in your browser and nothing is stored.
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