BMI Calculator
Body mass index
Enter your height and weight. Adult categories follow the CDC.
In short
How the BMI Calculator works
Body mass index (BMI) is weight in kilograms divided by height in meters squared. For adults aged 20 and over, the CDC classes a BMI under 18.5 as underweight, 18.5 to under 25 as healthy weight, 25 to under 30 as overweight, and 30 or more as obesity. BMI is a screening measure, not a diagnosis.
Guide
Adult BMI categories
For adults aged 20 and over, the CDC groups BMI into the categories below. The calculator assigns a category from your BMI rounded to one decimal place, so the number and the category you see always match.
| 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 or above | Obesity (class 3) |
Guide
The BMI formula
| Units | Formula | Example |
|---|---|---|
| Metric | weight (kg) / height (m)² | 70 kg / (1.75 m)² = 22.9 |
| US | 703 × weight (lb) / height (in)² | 703 × 160 lb / (70 in)² = 23.0 |
The calculator converts US units exactly (1 lb = 0.45359237 kg, 1 in = 2.54 cm), so both tabs give the same BMI for the same person. The familiar factor of 703 is that conversion rounded; the exact factor is about 703.07.
Guide
BMI Prime and Ponderal Index
BMI Prime is your BMI divided by 25, the upper limit of the healthy band, so a value from 0.74 to just under 1.00 falls in the healthy range. Ponderal Index divides weight by height cubed (kg/m³). It changes less with height than BMI does, which is why it is sometimes used for very tall or very short people.
Guide
What BMI does not tell you
BMI is a quick screening measure used across populations. It does not measure body fat directly and does not distinguish muscle from fat, so athletes and very muscular people can have a high BMI without excess fat. It also does not account for bone density, age, sex, ethnicity, pregnancy, or where fat is carried on the body. A healthcare provider can put a BMI result in context with other measures.
This calculator is for adults. Children and teens aged 2 to 19 are assessed with BMI-for-age percentiles; enter an age under 20 and the calculator points you to the CDC Child and Teen BMI Calculator instead of showing an adult category.
With documents
Questions
Frequently asked questions
What is the BMI formula?
BMI = weight (kg) / height (m)². In US units, BMI = 703 × weight (lb) / height (in)².
What is a healthy BMI range?
For adults, a BMI from 18.5 to under 25 is in the healthy weight category. The calculator also shows the weight range that corresponds to that band for your height.
What do the BMI categories mean?
They are screening bands used in population health. A result outside the healthy range is a reason to talk with a healthcare provider, not a diagnosis.
Is BMI accurate for athletes?
Not always. BMI does not separate muscle from fat, so muscular people can have a high BMI without excess body fat. It also does not account for bone density or where fat is carried.
Is BMI different for men and women?
The adult formula and categories are the same for everyone aged 20 and over. Body composition at a given BMI does differ by sex and age, which is one of BMI’s limitations.
Can I use this calculator for children?
No. Children and teens aged 2 to 19 are assessed with BMI-for-age percentiles, not the adult categories. Use the CDC Child and Teen BMI Calculator instead.
Sources
Method and review
The method is described on this page and every result shows how it was reached. Last reviewed by the PurePDF team. Spotted a mistake? Tell us.
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