BMI Calculator
Calculate body mass index with metric or US units. Includes adult BMI category, healthy weight range for your height, BMI Prime, and Ponderal Index.
BMI Result
BMI = 20.1 kg/m2
- Healthy BMI range (adults): 18.5 to less than 25
- Healthy weight for this height: 59.9 kg to 80.7 kg
- BMI Prime: 0.80
- Ponderal Index: 11.1 kg/m3
For ages 20+, adult BMI bands are shown. For ages 2-19, use BMI-for-age percentile charts.
BMI Classification (Adults)
The categories below follow the adult BMI ranges used in this calculator.
| Classification | BMI Range (kg/m2) |
|---|---|
| Underweight | Less than 18.5 |
| Healthy Weight | 18.5 to less than 25 |
| Overweight | 25 to less than 30 |
| Obesity | 30 or greater |
| Class 1 Obesity | 30 to less than 35 |
| Class 2 Obesity | 35 to less than 40 |
| Class 3 Obesity (Severe Obesity) | 40 or greater |
Children and Teens (Age 2 to 19)
For younger people, BMI is interpreted using BMI-for-age percentiles by sex and age, not adult cutoff values alone.
| Category | Percentile Range |
|---|---|
| Underweight | < 5th percentile |
| Healthy weight | 5th to < 85th percentile |
| Overweight | 85th to < 95th percentile |
| Obesity | ≥ 95th percentile |
Use CDC or local pediatric growth charts for official classification decisions.
BMI Formula
Metric (SI): BMI = weight (kg) / height^2 (m^2)
US customary: BMI = 703 x weight (lb) / height^2 (in^2)
BMI Prime: BMI / 25
Ponderal Index: weight (kg) / height^3 (m^3)
These formulas are implemented directly in this calculator and recalculated instantly when inputs change.
Limitations of BMI
BMI is useful as a fast screening indicator, but it does not directly measure body fat or fat distribution. Athletic build, age, sex, ethnicity, and medical context can all affect interpretation.
- High muscle mass can raise BMI without indicating excess fat.
- Older adults can have higher body fat at the same BMI as younger adults.
- Children and teens require age- and sex-specific percentile interpretation.
- Clinical decisions should combine BMI with additional measures and professional judgment.
Frequently Asked Questions
What does BMI measure?
Body mass index (BMI) estimates body weight relative to height. It is a screening metric, not a direct measure of body fat.
Can BMI be used for children and teens?
For ages 2 to 19, BMI should be interpreted with BMI-for-age percentiles and growth charts, not adult cutoff bands alone.
Is BMI accurate for athletes?
Not always. People with higher muscle mass can show elevated BMI without excess body fat, so additional measures are recommended.
What BMI range is considered healthy for adults?
For most adults, 18.5 to less than 25 is considered the healthy BMI range.
What is BMI Prime?
BMI Prime is your BMI divided by 25, the upper bound of the healthy adult BMI band in many guidelines.
What is Ponderal Index?
Ponderal Index uses height cubed instead of height squared and can provide an additional body-size reference, especially at height extremes.