Calculate your body mass index (BMI) in metric or imperial units using the standard formula. Shows your CDC weight category. For educational use only.
Formula: BMI = kg / m2. Imperial equivalent: (lb / in2) x 703. Source: CDC.
BMI does not directly measure body fat. See limitations below before interpreting your result.
Body mass index is a screening measure that uses height and weight to place adults into weight categories. It does not measure body fat directly, but it correlates with body fat at a population level and is widely used in clinical and public health settings.
For example, a person who weighs 70 kg and is 170 cm (1.70 m) tall has a BMI of 70 / (1.70 x 1.70) = 70 / 2.89 = 24.2.
| BMI | Weight Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obesity |
These categories apply to adults aged 20 and older. Children and teenagers are assessed using separate BMI-for-age growth charts.
The formula and weight categories used here come from the Centers for Disease Control and Prevention (CDC): About Adult BMI.
BMI is a population-level screening tool with well-documented limitations. It does not distinguish fat from muscle, bone, or fluid. It does not account for where fat is stored in the body, which affects health risk independently of overall weight. Research also shows that the standard cut-off values may not translate equally well across different ethnic groups. The CDC and many clinical guidelines note these limitations explicitly.
A person with a high BMI due to muscle mass may have lower health risk than someone of the same BMI with high abdominal fat. Conversely, people in the "healthy weight" BMI range can still have metabolic risk factors. For these reasons, a healthcare provider uses BMI alongside other clinical measures rather than in isolation.
See also: Body Surface Area (BSA) Calculator using the Mosteller formula, and LDL Cholesterol Calculator using the Friedewald equation.
BMI equals weight in kilograms divided by the square of height in meters: BMI = kg / m2. In imperial units, the equivalent is BMI = (weight in pounds / height in inches2) x 703. The CDC uses this formula for adults aged 20 and older.
The CDC defines four standard BMI ranges for adults: below 18.5 is underweight, 18.5 to 24.9 is healthy weight, 25.0 to 29.9 is overweight, and 30.0 or higher is obesity. These categories are reference thresholds, not a diagnosis.
BMI does not measure body fat directly. It does not distinguish between muscle and fat, and it does not account for differences in age, sex, ethnicity, or where fat is distributed in the body. Two people with the same BMI can have very different health profiles. A healthcare provider can place BMI in fuller clinical context.
Yes. For people under age 20, BMI is assessed using age- and sex-specific growth charts (BMI-for-age percentiles), not the adult cut-off values. This calculator uses the adult formula for ages 20 and older.
No. This tool calculates a number using a published formula. Only a qualified healthcare provider can diagnose a condition or recommend treatment.