BMI Calculator

Body Mass Index (BMI) is a simple numerical screening measure of body fat based on a person's weight and height. It is widely used by doctors, public health organizations, and fitness professionals because it is quick, cheap, and reasonably correlated with health outcomes for most adults. The metric formula is BMI = weight (kg) ÷ height (m)²; the imperial formula is BMI = (weight (lbs) ÷ height (in)²) × 703.

The World Health Organization (WHO) uses these standard adult categories: underweight (below 18.5), normal weight (18.5–24.9), overweight (25–29.9), and obese (30 and above). The colored indicator on this calculator shows where your value falls so you can see at a glance how close you are to a category boundary.

BMI has known limitations. It does not distinguish between muscle and fat, so very muscular athletes can score in the overweight or obese range despite low body fat. It also does not account for fat distribution, which matters for cardiovascular risk — abdominal fat is more dangerous than fat on the hips and thighs. BMI thresholds were derived primarily from European populations and may need adjustment for some Asian populations, where health risks rise at lower BMI values.

Use BMI as a starting point, not a diagnosis. If you are concerned about your weight, combine it with other measurements such as waist circumference, body fat percentage, and waist-to-hip ratio, and discuss the results with a healthcare professional. For children and teenagers, use age- and sex-specific BMI percentile charts rather than the adult cutoffs above.

Understanding what BMI does and does not measure helps you use it wisely. BMI is a screening tool, not a diagnostic test. It cannot distinguish between fat mass and lean mass, water weight, or bone density. A 6-foot bodybuilder weighing 220 pounds will register as obese by BMI, despite having 8% body fat. Conversely, an elderly person who has lost muscle mass may register as normal weight while carrying unhealthy amounts of fat. Always interpret BMI alongside other measurements.

Waist circumference is a powerful companion to BMI. Visceral fat (fat around abdominal organs) is metabolically active and strongly linked to cardiovascular disease, type 2 diabetes, and metabolic syndrome. Men with a waist over 40 inches (102 cm) and women over 35 inches (88 cm) face elevated risk regardless of BMI. The waist-to-hip ratio and waist-to-height ratio offer additional context.

Ethnicity affects BMI interpretation. The WHO suggests that for people of South Asian, Chinese, and other Asian descent, health risks rise at lower BMI values — overweight may begin at 23 and obesity at 27.5 rather than the standard 25 and 30 thresholds. Pacific Islander and some African populations may have different optimal ranges as well. Discuss your specific situation with a healthcare provider familiar with these distinctions.

Healthy weight management focuses on sustainable habits rather than rapid loss. Aim for 0.5–1 kg (1–2 lbs) per week through a modest calorie deficit, regular strength training to preserve muscle, adequate protein (about 1.6–2.2 g per kg of bodyweight for active adults), 7–9 hours of sleep, and stress management. Crash diets typically fail within a year and often result in regained weight plus lost muscle.