⚖️ BMI Calculator
Calculate BMI instantly in metric or imperial — with context on what the number means.
Our free BMI Calculator computes your Body Mass Index using the standard WHO formula and tells you which category you fall into. BMI is the most widely used screening tool for assessing body weight relative to height — but understanding its limitations is just as important as knowing your number.
The BMI Formula
Imperial: BMI = 703 × weight (lbs) ÷ height² (inches²)
Example Calculations
Metric: 70kg, 175cm tall: BMI = 70 ÷ (1.75)² = 70 ÷ 3.0625 = 22.9 (Normal weight)
Imperial: 154 lbs, 5'9" (69 inches): BMI = 703 × 154 ÷ (69)² = 108,262 ÷ 4,761 = 22.7 (Normal weight)
BMI Categories (WHO Standard)
- Below 18.5: Underweight — may indicate malnutrition, eating disorder, or other health issues
- 18.5 – 24.9: Normal weight — associated with lowest health risk in population studies
- 25.0 – 29.9: Overweight — moderately elevated risk for some conditions
- 30.0 – 34.9: Obese Class I — health screening recommended
- 35.0 – 39.9: Obese Class II — significantly elevated risk
- 40.0 and above: Severely obese (Class III) — high priority for clinical intervention
Important Limitations of BMI
BMI is a useful population-level screening tool but has well-documented limitations for individuals:
- Does not distinguish muscle from fat: A heavily muscled athlete and a sedentary person of the same height and weight have identical BMIs. Many professional athletes are classified as "overweight" by BMI.
- Does not measure fat distribution: Visceral fat (around organs) is far more metabolically harmful than subcutaneous fat (under the skin). BMI captures neither the location nor the type of fat.
- Ethnic variation: BMI thresholds were developed from European population data. Research shows Asian populations develop metabolic complications at lower BMI values, while some populations maintain better health at higher BMIs. Many health organizations now use adjusted thresholds for Asian patients.
- Age effects: Older adults naturally lose muscle and gain fat. A person in their 70s can have a "normal" BMI while having high body fat and low muscle mass (sarcopenic obesity).
Better Alternatives to BMI
- Waist circumference: Over 40 inches (102cm) for men, or 35 inches (88cm) for women, signals elevated metabolic risk regardless of BMI.
- Waist-to-height ratio: Divide your waist circumference by your height. A ratio above 0.5 is a strong predictor of cardiovascular risk and works better across ethnic groups than BMI.
- Body fat percentage: Measured by DEXA scan or the US Navy tape measure method. Directly measures body composition rather than approximating it. Healthy ranges: men 10–20%, women 18–28%.
⚖️ Calculate your BMI instantly — metric or imperial — with our free tool.
Open BMI Calculator →Frequently Asked Questions
Is a BMI of 25 considered overweight?
Yes, according to WHO classifications, a BMI of 25.0 to 29.9 falls in the "overweight" category. However, this is a statistical threshold based on population averages, not a diagnosis. Someone with a BMI of 25 may be perfectly healthy depending on their muscle mass, body fat distribution, and other health markers.
What is a healthy BMI for women vs men?
The WHO uses the same BMI categories for both men and women (18.5–24.9 is normal weight). However, women naturally carry more body fat than men at the same BMI due to hormonal and physiological differences. Body fat percentage ranges for "healthy" differ: men 10–20%, women 18–28%.
Can BMI be wrong?
Yes. BMI is an approximation based on height and weight alone. It is most useful as a population-level screening tool and least accurate for very muscular people, the elderly, children (who use different BMI-for-age charts), and people from certain ethnic backgrounds.