Calculate Your Body Mass Index
BMI is a screening tool to estimate body fat. Enter your weight and height below.
BMI Formula
BMI = weight (kg) / [height (m)]²
Or in US units: BMI = (weight in lb / [height in inches]²) × 703
WHO BMI Classification
- Underweight: BMI < 18.5
- Normal weight: BMI 18.5-24.9
- Overweight: BMI 25-29.9
- Obesity Class I: BMI 30-34.9
- Obesity Class II: BMI 35-39.9
- Obesity Class III: BMI ≥ 40
Limitations of BMI
BMI does not distinguish between muscle and fat. A bodybuilder may have high BMI (overweight or obese range) but low body fat. Conversely, someone with low muscle mass may have normal BMI but high body fat ("normal weight obesity").
BMI also does not account for fat distribution. Visceral fat (around organs) is more harmful than subcutaneous fat. Waist circumference and waist-to-hip ratio are better indicators of metabolic health.
For a more accurate body composition assessment, use body fat percentage.
References
Frequently asked questions
What is BMI?
Body mass index (BMI) is a screening tool that estimates body fat based on weight and height. BMI = weight (kg) / height (m)². The WHO classifies BMI: underweight (<18.5), normal (18.5-24.9), overweight (25-29.9), obese (≥30).
Is BMI accurate?
BMI is a rough screening tool, not a diagnostic measure. It does not distinguish between muscle and fat. Athletes with high muscle mass may have high BMI but low body fat. BMI also does not account for age, sex, or fat distribution. Body fat percentage and waist circumference are more accurate health indicators.
What is a healthy BMI?
A BMI of 18.5-24.9 is considered normal weight for most adults. However, BMI should be used alongside other measures like waist circumference, body fat percentage, and overall health markers (blood pressure, cholesterol, blood sugar).