BMI Calculator
BMI = 20.1 kg/m² (Normal)
- BMI
- 20.1 kg/m²
- Category
- Normal
- Healthy BMI range
- 18.5 – 25 kg/m²
- Healthy weight for height
- 59.9 – 81 kg
- BMI Prime
- 0.8
- Ponderal Index
- 11.1 kg/m³
What this BMI calculator does
Body mass index (BMI) is a screening measure that compares weight with height. It is widely used because it is quick, inexpensive, and does not require body composition equipment. This calculator reports BMI, the standard category, the healthy weight range for your height, BMI Prime, and the ponderal index.
BMI is not a diagnosis. It does not measure body fat directly, and it can misclassify athletes, older adults, pregnant people, and people with very high or very low muscle mass.
How to use this calculator
- Choose US Units, Metric Units, or Other Units. Other Units opens the Conversion Calculator if you need to convert height or weight first.
- Enter your age and sex. The BMI formula itself uses only height and weight, but the fields are included for reference.
- Enter your height. In US units, use feet and inches; in metric units, use centimeters.
- Enter your weight in pounds or kilograms.
- Click Calculate to see your BMI, the BMI scale, and the healthy weight range for your height.
The default example uses metric units: a 25-year-old man who is 180 cm tall and weighs 65 kg.
BMI formulas
BMI = weight (kg) ÷ height (m)²
BMI Prime = BMI ÷ 25
Ponderal index = weight (kg) ÷ height (m)³
Healthy weight range = 18.5 × height (m)² to 25 × height (m)²
| Classification | BMI range (kg/m²) |
|---|---|
| Severe thinness | Below 16.0 |
| Moderate thinness | 16.0–16.9 |
| Mild thinness | 17.0–18.4 |
| Normal | 18.5–24.9 |
| Overweight | 25.0–29.9 |
| Obese class I | 30.0–34.9 |
| Obese class II | 35.0–39.9 |
| Obese class III | 40.0 and above |
BMI Prime adds a second way to read the same bands:
| Classification | BMI | BMI Prime |
|---|---|---|
| Severe thinness | Below 16.0 | Below 0.64 |
| Moderate thinness | 16.0–16.9 | 0.64–0.68 |
| Mild thinness | 17.0–18.4 | 0.68–0.74 |
| Normal | 18.5–24.9 | 0.74–1.0 |
| Overweight | 25.0–29.9 | 1.0–1.2 |
| Obese class I | 30.0–34.9 | 1.2–1.4 |
| Obese class II | 35.0–39.9 | 1.4–1.6 |
| Obese class III | 40.0 and above | Above 1.6 |
For children and teenagers, BMI is interpreted with age- and sex-specific percentiles:
| Category | Percentile range |
|---|---|
| Underweight | Below 5% |
| Healthy weight | 5%–85% |
| At risk of overweight | 85%–95% |
| Overweight | Above 95% |
What the results mean
- BMI: weight relative to height. The default example is 20.1, which is in the normal range.
- Category: the standard BMI band for the result.
- Healthy weight range: the weight range that would produce a BMI between 18.5 and 25 at your height. For the default metric example, it is 59.9–81 kg.
- BMI Prime: BMI divided by 25. A value below 1.0 is within the upper limit of the normal range; for example, 0.8 means the BMI is 80% of that limit.
- Ponderal index: weight divided by height cubed. It is an alternative measure that can be more stable at extreme heights.
Assumptions and limitations
BMI assumes a typical body composition and does not distinguish fat from muscle or bone. It does not account for age-related changes in body composition, pregnancy, athletic training, or medical conditions. It is also not a complete assessment of health: blood pressure, cholesterol, blood glucose, waist circumference, and lifestyle all matter.
The healthy weight range is based on a BMI of 18.5 to 25 for adults. Children and teenagers use age- and sex-specific BMI percentiles; the table above shows the usual bands, but this calculator does not compute them.
Frequently asked questions
Is BMI accurate for athletes?
Not always. Muscle is denser than fat, so a muscular athlete can have a high BMI without excess body fat. A body composition measurement or waist circumference can add context.
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is classified as normal. The healthy weight range shown by the calculator translates that band into pounds or kilograms for your height.
Does BMI work for children?
No. Children and teenagers are assessed with age- and sex-specific BMI percentiles, not the adult categories used here.
Is BMI a diagnosis?
No. It is a screening tool. A clinician considers BMI together with medical history, waist circumference, blood pressure, laboratory results, and other factors.
Source
References:
Disclaimer
This calculator is for informational and educational purposes only. It is not medical advice or a diagnosis. Discuss your weight, body composition, and health risks with a qualified clinician.