BMI Calculator

Your body mass index, your category, and your healthy weight range — plus an honest section on what BMI genuinely can't tell you.

What BMI is — and the one thing it measures well

BMI is weight divided by height squared (kg/m²) — a formula from the 1830s designed by a statistician, not a physician, to describe populations. At the population level it works: average BMI tracks average body fat well enough that health agencies use it for screening. The categories above are the WHO's standard cutoffs, and this calculator inverts the formula to show the weight range that maps to "normal" for your height.

Where BMI honestly fails

BMI cannot see body composition, and that produces predictable false readings for specific groups. Worth stating plainly:

• Muscular people read as overweight. Muscle is denser than fat; a lean, strength-trained 5'10" man at 195 lb has a BMI of 28 — "overweight" — with less body fat than many people in the "normal" band.
• "Normal" can hide high body fat. Low muscle mass plus high fat — common with age and sedentary living — can produce a healthy-looking BMI alongside genuinely elevated metabolic risk. Clinicians call it normal-weight obesity.
• It ignores where fat sits. Abdominal (visceral) fat carries far more risk than fat elsewhere; two people with identical BMIs can have very different risk profiles. A tape measure at the waist adds information BMI can't: waist over half your height is a widely used warning threshold.
• Cutoffs weren't built for everyone. Risk appears at lower BMIs in many Asian populations (several countries use 23 as the overweight line) and the standard cutoffs fit older adults poorly.

The honest summary: a BMI of 40 means something in any population, a BMI of 27 means almost nothing without more context. Treat the number as a prompt to look closer, never as a diagnosis.

Better questions than "what's my BMI?"

If you're using BMI to guide eating or training decisions, two other numbers do more work. Your TDEE tells you what your body actually burns per day — the foundation of any deliberate weight change. And if a change is the goal, the rate of change matters more than most people think: our article on safe calorie deficits explains why the sustainable deficit beats the aggressive one, and TDEE vs. BMR untangles the two numbers calculators throw around.

Questions people ask

Is BMI useless, then?

No — it's free, instant, and correct on average. For a sedentary adult of typical build, the category is usually in the right neighborhood. It's the edge cases — athletes, older adults, certain ethnic groups — where it misleads, and the failure modes are known and predictable.

What's a better single measurement?

Waist-to-height ratio costs a tape measure and beats BMI in most studies of metabolic risk prediction. Keeping your waist under half your height is the memorable version.

My BMI says underweight — should I worry?

Unintentional weight loss or a BMI drifting below 18.5 without explanation is worth a doctor's visit — underweight carries real risks that get less attention than overweight. If you're a naturally light "hard gainer" trying to add weight, the TDEE calculator's lean-gain target is the starting point.