BMI Calculator
Calculate your Body Mass Index, BMI Prime, Ponderal Index, and healthy weight range using metric or imperial units.
Body Mass Index
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BMI Prime
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Ponderal Index
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Healthy Weight Range
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| WHO Category | BMI Range |
|---|---|
| Severe Thinness | < 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 |
What is BMI Calculator?
BMI (Body Mass Index) is a number calculated from your height and weight that gives a general indication of whether your weight falls in a healthy range. It is widely used as a screening tool by healthcare professionals, though it doesn't directly measure body fat or account for muscle mass. BMI Prime is the ratio of your BMI to the upper limit of normal (25), so a BMI Prime of 1.0 means you are exactly at the top of the normal range. The Ponderal Index (also called Corpulence Index) is similar to BMI but uses the cube of height, making it less sensitive to height extremes.
How to use
- 1 Choose between Metric (cm, kg) or Imperial (feet, inches, lbs) using the toggle.
- 2 Enter your age, height, and weight in the appropriate fields.
- 3 Your BMI, BMI Prime, Ponderal Index, and healthy weight range appear instantly.
- 4 Use the WHO classification table to understand your BMI category.
Formula
Example calculation
A person who is 175 cm tall and weighs 70 kg has a BMI of 70 / (1.75)² = 22.9 (Normal). BMI Prime = 22.9 / 25 = 0.92. Ponderal Index = 70 / (1.75)³ = 13.1. Healthy weight range for 175 cm: 56.7 – 76.3 kg.
Frequently asked questions
What is a healthy BMI range?
A BMI between 18.5 and 24.9 is considered normal weight by WHO standards. Below 18.5 is underweight (with further tiers below 17 and 16), 25–29.9 is overweight, and 30 or above is classified as obese (with three obesity classes).
What is a healthy BMI for my age?
For adults 20 and older, standard BMI categories apply regardless of age. However, for older adults (65+), some studies suggest a slightly higher BMI (between 23 and 27) may be healthier and protective. For children and teens under 20, BMI is interpreted using age- and sex-specific percentiles.
What is BMI Prime?
BMI Prime is your BMI divided by 25 (the upper limit of normal). A value below 1 means you are in or below the normal range; a value above 1 means you are overweight or obese. For example, a BMI of 27.5 gives a BMI Prime of 1.10, indicating 10% above the normal upper limit.
What is the Ponderal Index?
The Ponderal Index (PI) = weight(kg) / height(m)³. It was proposed as an alternative to BMI because it is less sensitive to height variations. The normal range is approximately 11–15 kg/m³. It is less commonly used clinically but can give a different perspective for very tall or very short individuals.
Is BMI accurate for athletes?
BMI can overestimate body fat in muscular individuals like athletes, since muscle weighs more than fat. A high BMI in an athlete may not indicate excess body fat. Body fat percentage measurements are more informative in that case.
Does BMI apply to children?
BMI for children and teenagers is calculated the same way but interpreted using age- and sex-specific percentile charts, not the standard adult cutoffs.
Can BMI differ between ethnic groups?
Yes. Research suggests that health risks associated with higher body fat may occur at lower BMI thresholds for some Asian populations. Some guidelines use adjusted cutoffs for these groups.