BMI Calculator
Calculate your Body Mass Index to understand if your weight is in a healthy range for your height. Supports both metric and imperial units.
Your BMI
24.2
Normal
Healthy Range
53.5 – 72.0 kg
BMI Prime
0.97
Ponderal Index
14.2 kg/m³
Health Disclaimer
BMI is a screening tool, not a diagnostic measure. It does not account for muscle mass, bone density, age, sex, or ethnicity. Athletes and muscular individuals may have a high BMI despite low body fat. Always consult a healthcare professional for a complete health assessment.
Understanding BMI
Body Mass Index (BMI) is the most widely used screening tool for weight classification. Developed by Belgian mathematician Adolphe Quetelet in the 1830s, it provides a simple numeric measure of a person's thickness or thinness based on their mass and height.
BMI Formulas
Metric
BMI = weight (kg) ÷ height² (m²) Imperial
BMI = (weight (lbs) × 703) ÷ height² (in²) WHO BMI Classification (Adults)
| Category | BMI Range | Health Risk |
|---|---|---|
| Severe Thinness | < 16.0 | High |
| Moderate Thinness | 16.0 – 16.9 | Moderate |
| Mild Thinness | 17.0 – 18.4 | Low |
| Normal | 18.5 – 24.9 | Low |
| Overweight | 25.0 – 29.9 | Increased |
| Obese Class I | 30.0 – 34.9 | High |
| Obese Class II | 35.0 – 39.9 | Very High |
| Obese Class III | ≥ 40.0 | Extremely High |
Limitations of BMI
While BMI is useful as a quick screening tool, it has known limitations:
- Does not measure body fat directly — a bodybuilder and an obese person can have the same BMI
- Does not account for muscle mass — athletes often score as "overweight"
- Age-related changes — older adults lose muscle, so BMI may underestimate fat
- Ethnic variations — Asian populations have higher risk at lower BMI values
- Sex differences — women typically have more body fat than men at the same BMI
- Does not indicate fat distribution — visceral (belly) fat is riskier than subcutaneous fat
Better Alternatives to BMI
For a more complete picture, consider these additional measurements:
- Waist circumference: >40 in (men) or >35 in (women) indicates higher health risk
- Waist-to-hip ratio: more predictive of cardiovascular risk than BMI alone
- Body fat percentage: measured via DEXA scan, calipers, or bioelectrical impedance
- Waist-to-height ratio: keep your waist less than half your height
Frequently Asked Questions
What is BMI and what does it measure?
Body Mass Index (BMI) is a numerical value calculated from your weight and height. It provides a simple screening metric to categorize individuals as underweight, normal weight, overweight, or obese. BMI does not directly measure body fat percentage but correlates with more direct measures of body composition at a population level.
How is BMI calculated?
BMI is calculated by dividing weight in kilograms by height in meters squared: BMI = kg/m². For imperial units, the formula is: BMI = (weight in pounds × 703) / (height in inches)². For example, a person weighing 70 kg at 170 cm height has a BMI of 70 / (1.70)² = 24.2.
What is a healthy BMI range?
According to the World Health Organization (WHO), a healthy BMI is between 18.5 and 24.9. Below 18.5 is considered underweight, 25-29.9 is overweight, and 30 or above is classified as obese. These thresholds apply to adults aged 20 and older.
Is BMI accurate for everyone?
BMI has limitations. It may overestimate body fat in athletes and muscular individuals, and underestimate it in older adults who have lost muscle mass. It also does not account for differences in body composition between ethnic groups, sexes, or age groups. South Asian and East Asian populations may have higher health risks at lower BMI thresholds.
What is BMI Prime?
BMI Prime is the ratio of your actual BMI to the upper limit of the normal range (25). A BMI Prime of 1.0 means you are at the upper boundary of healthy weight. Values below 1.0 are healthy; above 1.0 indicates overweight. It provides a quick way to see how far from the healthy threshold you are.
Does BMI apply to children and teenagers?
For children and teens (ages 2-20), BMI is calculated the same way but interpreted differently using age-and-sex-specific percentile charts (BMI-for-age). A child at the 85th-95th percentile is considered overweight; above the 95th percentile is obese. This calculator is designed for adults.
What should I do if my BMI is outside the healthy range?
If your BMI indicates you are overweight or underweight, consult a healthcare provider. They can assess your overall health using additional measures like waist circumference, body fat percentage, blood work, and medical history. BMI alone should not be used to make health decisions.
What is the Ponderal Index?
The Ponderal Index (PI) is an alternative to BMI that uses height cubed instead of squared: PI = weight(kg) / height(m)³. It is considered more appropriate for very tall or very short individuals where BMI may be misleading. A normal PI is approximately 11-15 kg/m³.