BMI Calculator: Check Your Body Mass Index
Free online BMI calculator and web app. Check your body mass index, see your weight category and find your healthy weight range. Install it on your phone like an app.
What is BMI?
Body Mass Index (BMI) is a quick screening measure that compares your weight to your height. It is widely used by doctors and health organizations to group adults into weight categories and to flag possible health risks.
BMI formula
| Units | Formula |
|---|---|
| Metric | BMI = weight (kg) / height (m)² |
| US | BMI = 703 x weight (lb) / height (in)² |
Example: a person who weighs 70 kg and is 175 cm tall has a BMI of 70 / (1.75 x 1.75) = 22.9, which is in the healthy range.
BMI categories for adults
| Category | BMI |
|---|---|
| Severe thinness | below 16 |
| Moderate thinness | 16 - 16.9 |
| Mild thinness | 17 - 18.4 |
| Healthy weight | 18.5 - 24.9 |
| Overweight | 25 - 29.9 |
| Obese class I | 30 - 34.9 |
| Obese class II | 35 - 39.9 |
| Obese class III | 40 and above |
Limits of BMI
BMI does not measure body fat directly and cannot tell muscle from fat. Athletes, older adults and people with different body builds may get a misleading result. For a fuller picture, also look at waist circumference, body fat percentage and overall health. This calculator also shows BMI Prime (your BMI divided by 25) and the Ponderal Index (weight divided by height cubed).
What to do next
If you want to change your weight, start by finding your daily energy needs with our TDEE Calculator or the Calorie Calculator, or browse all free tools.
Frequently asked questions
What is BMI?
Body mass index (BMI) is your weight in kilograms divided by your height in meters squared. It is a simple screening number used to place adults in weight categories.
What is a healthy BMI?
For adults, the World Health Organization defines a healthy BMI as 18.5 to 24.9. Below 18.5 is underweight, 25 to 29.9 is overweight and 30 or above is obese.
How is BMI calculated?
In metric units, BMI = weight (kg) / height (m) squared. In US units, BMI = 703 x weight (lb) / height (in) squared. For example, 70 kg at 175 cm gives a BMI of 22.9.
Is BMI accurate for athletes and muscular people?
Not always. BMI cannot tell muscle from fat, so very muscular people can read as overweight. Age, sex and ethnicity also matter, so use BMI together with waist size and body fat.
Does this BMI calculator work for children?
No. This calculator is for adults aged 18 and over. For ages 2 to 19, BMI is interpreted with percentile charts for age and sex, such as the CDC growth charts.
What should I do if my BMI is outside the healthy range?
BMI is a screening tool, not a diagnosis. Talk to a doctor or registered dietitian, who can look at your waist size, health history and lifestyle before suggesting changes.
Disclaimer: This calculator gives estimates for general information only and is not medical advice. Consult a doctor or registered dietitian before major diet changes.
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