BMI Calculator
Body Mass Index (BMI) is a screening measurement that estimates whether your weight is healthy for your height, calculated as weight in kilograms divided by height in meters squared. It's used by doctors and public health bodies like the WHO and CDC as a quick, low-cost first check, not a diagnostic tool, since it doesn't directly measure body fat.
Interactive tool
Calculate Your BMI
BMI is a general screening tool, not a medical diagnosis. It doesn't account for muscle mass, bone density, or fat distribution. Talk with a doctor or registered dietitian to understand what your BMI means for your individual health.
How Is BMI Calculated?
BMI is calculated with a simple formula: BMI = weight (kg) ÷ height (m)². In plain English, you divide your weight in kilograms by your height in meters, then divide that result by your height in meters again.
If you use pounds and inches, the formula adjusts to: BMI = (weight in pounds ÷ height in inches²) × 703.
Weight: 70 kg — Height: 1.75 m
70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625
BMI = 22.86 → Healthy weight
BMI Categories (WHO / CDC Standard Ranges)
These are the standard adult BMI weight categories used by the World Health Organization and the U.S. CDC:
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
Limitations of BMI
BMI is a useful screening tool, but it has well-documented limits. It doesn't distinguish between muscle and fat, so muscular people can register as "overweight" despite low body fat. It also doesn't account for bone density, age-related muscle loss, or where fat is stored on the body, which affects health risk.
BMI's standard cutoffs were developed primarily on data from European populations. Both the WHO and CDC note that health risk at a given BMI can vary by ethnicity, sex, and age, so BMI should be treated as one input among several, not a standalone diagnosis.
Frequently Asked Questions
What is a healthy BMI for my height?
A healthy BMI for adults is between 18.5 and 24.9, regardless of height, because BMI already adjusts for height in its formula. Enter your height into the calculator above to see the exact healthy weight range in kilograms or pounds for your specific height.
Is BMI accurate for athletes?
BMI can be misleading for athletes and other very muscular people. Because muscle is denser than fat, a muscular person can have a high BMI while carrying very little body fat, so BMI may overestimate their health risk.
How is BMI different from body fat percentage?
BMI estimates whether your weight is appropriate for your height using a simple formula. Body fat percentage measures the actual proportion of fat in your body, typically using skinfold calipers, bioelectrical impedance scales, or a DEXA scan.
Does BMI mean different things for men and women?
The WHO BMI categories use the same numeric ranges for men and women. However, women naturally carry a higher percentage of body fat than men at the same BMI, so BMI alone doesn't fully capture body composition differences between sexes.
What BMI is considered obese?
According to WHO and CDC standards, a BMI of 30 or higher falls into the obese category for adults. A BMI of 40 or above is sometimes further classified as severe or Class III obesity.
Can I use BMI for children or teenagers?
No. Standard adult BMI categories don't apply to children and teens, since healthy body fat changes as kids grow. The CDC recommends age- and sex-specific BMI-for-age growth charts and percentiles instead for anyone under 18.