Calculate your Body Mass Index (BMI) to check if your weight is healthy for your height. Supports both metric and imperial units.
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What BMI Tells You — and What It Does Not
BMI (Body Mass Index) is calculated by dividing weight in kilograms by height in meters squared. WHO classifies results as: under 18.5 = Underweight, 18.5–24.9 = Normal weight, 25–29.9 = Overweight, 30+ = Obese. BMI is a useful population-level screening tool but has important limitations: it cannot distinguish between muscle and fat mass, does not account for fat distribution (waist circumference matters), and uses the same ranges for different ethnicities despite evidence that health risks vary by population. Use BMI as a starting point alongside waist circumference and other health indicators.
How BMI Is Calculated
BMI = weight (kg) / height² (m²). Example: 80 kg at 1.75 m = 80 / 3.0625 = 26.1 (Overweight). In imperial: BMI = (weight in lbs / height in inches²) × 703. Enter your measurements above and toggle between metric (kg/cm) and imperial (lbs/ft-in) units. Results show your BMI number, weight category, and how many kg/lbs above or below the top of the normal weight range you currently are.
Frequently Asked Questions
WHO standard: Underweight = below 18.5. Normal weight = 18.5–24.9. Overweight = 25–29.9. Obese Class I = 30–34.9. Obese Class II = 35–39.9. Obese Class III (severe) = 40+. These ranges apply to adults age 20+. Children use age and sex-specific BMI percentile charts.
BMI = weight in kg / (height in m)². Example: 75 kg at 1.75 m = 75 / (1.75 × 1.75) = 75 / 3.0625 = 24.5. Imperial formula: (weight in lbs / height in inches²) × 703. Example: 165 lbs at 69 inches = (165 / 4,761) × 703 = 24.4.
BMI uses only weight and height — it cannot distinguish muscle from fat. A muscular athlete may weigh more than a sedentary person of the same height, producing a higher BMI despite having a lower body fat percentage and better metabolic health. Body fat percentage measurement (DEXA scan or skinfold calipers) is more accurate for athletes.
Research shows that health risks (diabetes, cardiovascular disease) occur at lower BMI levels in South Asian and East Asian populations. Some guidelines use a lower overweight threshold of 23 for South Asians. WHO acknowledges this limitation of universal BMI cutoffs but maintains the standard ranges for global consistency.
Consult your doctor — BMI is a screening tool, not a diagnosis. Your doctor will assess additional risk factors: waist circumference, blood pressure, cholesterol, blood sugar, and activity level. A structured approach combining dietary changes and physical activity, ideally with professional guidance, is more effective than focusing on BMI alone.
