BMI Calculator

How to Calculate BMI

BMI is your weight divided by your height squared. In metric: BMI = weight (kg) / height (m)². In imperial: BMI = (weight (lb) / height (in)²) × 703.

Worked example: someone 5'9" (69 inches) weighing 160 lb. Square the height: 69 × 69 = 4,761. Divide weight by that: 160 / 4,761 = 0.0336. Multiply by 703: 23.6, squarely in the healthy range. The calculator above does this instantly and shows where you land on the scale.

What Your BMI Means

The World Health Organization categories for adults: under 18.5 is underweight, 18.5 to 24.9 is the healthy range, 25 to 29.9 is overweight, and 30 or above is obese (30-34.9 class I, 35-39.9 class II, 40+ class III). These are screening cutoffs used across population health, not a diagnosis of any individual.

The calculator also shows your healthy weight range for your height: the weights that would put your BMI between 18.5 and 24.9. That range is often more useful than the single number, because it gives you a target zone instead of a pass/fail.

What BMI Gets Wrong

BMI cannot tell muscle from fat. A lifter with low body fat can score as overweight; an older adult with little muscle can score as healthy while carrying risky visceral fat. It also ignores where fat sits (belly fat carries more risk than hip fat), and the standard cutoffs were built mainly from European populations. Some health authorities use lower thresholds for Asian populations.

Children and teens use BMI percentiles, not fixed cutoffs. Pregnancy, elite athletic training, and significant muscle loss with age all make the standard categories misleading. Doctors treat BMI as a starting screen alongside waist circumference, blood work, and an actual conversation, never as a verdict on its own. For the full picture, read our guide to calculating and interpreting BMI.

Who Uses a BMI Calculator

People starting a fitness or weight-loss plan use it as a baseline to measure against later. Doctors and nurses record it at checkups as a quick screen. Life and health insurance applications often ask for it. Coaches use it with clients to set realistic targets, and curious searchers just want to know where they stand. Whatever brought you here, the number is a starting point for a conversation, ideally with a professional, not a final answer.