BMI Calculator

BMI is the most widely used weight classification tool in clinical medicine — not because it's the most accurate measure of health, but because it requires only two measurements that everyone has. Enter your weight and height, and you get a number that places you in a category compared to millions of people. What that number doesn't tell you is whether your weight is fat or muscle, where your fat is located, or how your metabolic markers look. The BMI calculator gives you your number and its category — understanding the context is what makes it useful.

The BMI Formula and What It Measures

BMI = weight (kg) / height (m)²

In imperial units: BMI = (weight in lbs / height in inches²) × 703

A 70 kg person who is 1.75 m tall: BMI = 70 / (1.75)² = 70 / 3.0625 = 22.9 — normal weight. The same weight at 1.60 m: BMI = 70 / 2.56 = 27.3 — overweight. Height is squared because body surface area (which correlates with weight) scales with the square of linear dimensions. BMI increases with weight, decreases with height. Use this online calculator for your exact numbers. The BMR calculator estimates how many calories your body burns at rest.

WHO BMI Categories for Adults

• Below 18.5: Underweight — increased risk of nutritional deficiency, weakened immune function, bone density loss
• 18.5–24.9: Normal weight — lowest risk for weight-related chronic diseases in population studies
• 25.0–29.9: Overweight — moderately elevated risk for type 2 diabetes, hypertension, cardiovascular disease
• 30.0–34.9: Obese Class I — substantially elevated metabolic risk
• 35.0–39.9: Obese Class II — high risk
• 40.0+: Obese Class III (severe obesity) — very high risk for all weight-related conditions

What BMI Misses — And Better Alternatives

BMI's biggest weakness is that it doesn't distinguish fat from muscle or measure fat distribution. A 200-lb bodybuilder at 5'10" has a BMI of 28.7 — "overweight" — despite having very low body fat and excellent metabolic health. An inactive person at the same BMI with 35% body fat may have metabolic syndrome. Better alternatives for individual assessment:

• Waist circumference: above 35 inches (women) or 40 inches (men) indicates abdominal obesity and elevated metabolic risk regardless of BMI
• Waist-to-height ratio: keep your waist below half your height for general health guidance (below 0.5)
• Body fat percentage by DEXA: gold standard for body composition assessment
• Metabolic panel: blood glucose, lipids, blood pressure — these directly measure metabolic health

The body fat calculator and body metrics calculators provide complementary tools beyond BMI.

Asian Population BMI Thresholds

Research consistently shows that people of East and South Asian descent develop metabolic complications (type 2 diabetes, cardiovascular disease) at lower BMI values than European populations. The WHO expert consultation (2004) recommended action points of 23.0 for overweight and 27.5 for obesity in Asian populations, and these thresholds are used in clinical practice in many Asian countries. A BMI of 25 in a Japanese person carries higher metabolic risk than the same BMI in a Northern European — this isn't a flaw in the population but a limitation of using a single global threshold derived primarily from European cohorts.