Body mass index (BMI) is a quick screening number that compares your weight with your height. Use this free calculator to find your BMI, see which category it falls into and learn the healthy weight range for your height. Choose metric (kilograms and centimeters) or US units (pounds, feet and inches).
How BMI is calculated
BMI equals your weight in kilograms divided by your height in meters squared. In US units, it is your weight in pounds multiplied by 703 and divided by your height in inches squared. For example, a person who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.
BMI categories 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 |
| 40.0 and above | Obesity, class 3 |
What BMI can and cannot tell you
BMI is simple and free, which is why doctors use it as a first screening step. But it is only a rough guide:
- It does not measure body fat. Muscular people and athletes can have a high BMI without excess fat.
- It ignores where fat is stored. Fat around the waist carries more health risk than fat on the hips and thighs. Waist circumference adds useful information; risk rises above about 102 cm (40 in) for men and 88 cm (35 in) for women.
- It can read differently with age. Older adults lose muscle, so a “healthy” BMI may hide low muscle mass.
- Some ethnic groups face higher risk at lower BMI. The WHO notes that for many people of Asian descent, health risks increase at lower BMI values.
- Children and teens are different. Their BMI is compared with growth charts for their age and sex.
If your BMI is outside the healthy range, it is a prompt to look at the bigger picture with a healthcare professional: your waist size, blood pressure, blood sugar, cholesterol, fitness and family history.
Small steps that support a healthy weight
- Build a daily walking habit. See how much walking you really need.
- Eat more fiber-rich foods. Our guide to fiber explains how.
- Protect your sleep: short sleep is linked to weight gain. Try our 8 sleep habits.
- Estimate your daily energy needs with the calorie calculator.
Frequently asked questions
What is a healthy BMI?
For most adults, a BMI from 18.5 to 24.9 is considered the healthy range. It is a general guide, not a verdict on your health.
Is BMI accurate for athletes?
Not always. Because muscle weighs more than fat, very muscular people can have a BMI in the overweight range with low body fat. A body-fat estimate, such as our body fat calculator, may be more informative.
Is the BMI formula different for men and women?
No. The adult formula and categories are the same for men and women, although men and women of the same BMI tend to have different amounts of body fat.
Can I use BMI for my child?
The number is calculated the same way, but it must be compared with age- and sex-specific growth charts. Ask your child’s pediatrician to interpret it.
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This calculator provides general estimates for healthy adults and is for information only. It is not medical advice and does not replace a conversation with a qualified healthcare professional. Read our disclaimer and editorial policy.