Body Mass Index · Healthy weight range · Ideal weight · Imperial & metric · Adults
What Is BMI and How Is It Calculated?
Body Mass Index (BMI) is calculated by dividing your weight in kilograms by the square of your height in meters: BMI = kg/m². For imperial units: BMI = (lbs × 703) / (inches²). It provides a simple numerical measure of body fatness relative to height and is widely used by healthcare professionals as an initial screening tool for weight-related health conditions.
BMI Limitations — What It Doesn't Tell You
- Muscle vs fat — A muscular athlete can have a "overweight" BMI with very low body fat. BMI can't distinguish between lean mass and fat mass.
- Fat distribution — Where fat is stored matters. Abdominal fat carries higher cardiovascular risk than the same BMI with fat stored elsewhere.
- Age and gender — Older adults and women typically have more body fat at the same BMI. Children use age-specific percentile charts.
- Ethnicity — Some research suggests Asian populations may face health risks at lower BMI thresholds (risk begins at ~23 vs 25 for other groups).
Better Metrics to Use Alongside BMI
- Waist circumference — Risk increases above 35 inches (women) or 40 inches (men)
- Waist-to-height ratio — Should be below 0.5 for most adults
- Body fat percentage — Measured via DEXA scan, hydrostatic weighing, or skinfold calipers
- Waist-to-hip ratio — WHO risk classification: above 0.90 (men) or 0.85 (women) indicates abdominal obesity
Frequently Asked Questions
What is a healthy BMI for adults?
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According to the World Health Organization, a healthy BMI for most adults is between 18.5 and 24.9. Below 18.5 is classified as underweight; 25–29.9 is overweight; 30 and above is obese. However, these thresholds are population-level guidelines. Individual health status depends on many factors beyond BMI including fitness level, blood markers, and metabolic health.
Is BMI accurate for athletes and muscular people?
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No — BMI significantly overestimates body fat in highly muscular individuals. A 200-pound athlete at 5'10" has a BMI of 28.7 (overweight) but may have only 10–12% body fat. For athletes, body composition testing (DEXA, hydrostatic weighing, or bioelectrical impedance) is a much more accurate health indicator than BMI alone.
How can I lower my BMI?
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BMI decreases when you lose body fat, which requires a caloric deficit over time. A deficit of 500 calories/day leads to approximately 1 pound of fat loss per week. Combining reduced caloric intake with resistance training is optimal — it preserves muscle mass while reducing fat, which improves body composition even if BMI changes slowly. Use our Calorie Calculator to find your daily needs.