BMI Calculator
Calculate your BMI and understand what it means, with context about its limitations.
BMI is a useful population-level screening tool that is widely misused at the individual level. It tells you roughly where you sit on a weight distribution for your height. What it can't tell you is whether that weight is muscle or fat, or where the fat is stored, both of which matter far more for health than the number itself.
BMI categories: Underweight (<18.5), Normal (18.5–24.9), Overweight (25–29.9), Obese (30+). These are population thresholds, not individual diagnoses. A muscular athlete can have an "obese" BMI with low body fat.
What BMI measures, and what it doesn't
BMI (Body Mass Index) = weight in kg ÷ (height in meters)². It's a simple ratio of weight to height that correlates roughly with body fat at the population level. Its limitations at the individual level are well-documented: it doesn't distinguish muscle from fat, doesn't account for fat distribution (visceral vs subcutaneous), produces different health risk predictions for different ethnic groups, and systematically misclassifies muscular individuals as overweight or obese.
When BMI is useful
BMI is most useful as a quick, costless screening tool for population health and for tracking weight trends over time in an individual. The BMI category thresholds were derived from population mortality data, people with BMIs in the overweight and obese ranges have higher average rates of cardiovascular disease, type 2 diabetes, and other metabolic conditions. But these are statistical associations across populations, not deterministic predictions for any individual.
Better metrics for individual health
Waist-to-height ratio, waist circumference, body fat percentage (via DEXA or the Navy method), and metabolic health markers (blood pressure, fasting glucose, HDL cholesterol, triglycerides) are all more informative for individual health assessment than BMI. The combination of normal waist-to-height ratio and healthy metabolic markers predicts cardiovascular health better than BMI alone.
Frequently asked questions
Is BMI the same for men and women?
The BMI formula and thresholds are the same, but women typically have higher body fat at the same BMI than men due to differences in body composition. Some researchers argue sex-specific BMI thresholds would be more accurate, but the standard thresholds are universally applied.
Are there different thresholds for Asian populations?
Yes. Research has found that metabolic risk increases at lower BMI values in South and East Asian populations. The World Health Organization and some national health organizations recommend lower cutoffs for these groups: overweight at ≥23 and obese at ≥27.5 in some Asian contexts.