BodyCalWhat this BMI calculator does
Enter your height and weight and you instantly get your Body Mass Index, your WHO weight category, the healthy weight range for your specific height, and an animated scale showing exactly where you sit between underweight, healthy, overweight, and obese. No tables to squint at, no unit conversions to do by hand — metric and imperial are one tap apart.
How the BMI formula works
BMI was devised in the 1830s by Adolphe Quetelet and remains the most widely used weight screening metric in medicine. The formula is simple:
- BMI = weight (kg) ÷ height (m)²
- In imperial units: BMI = 703 × weight (lb) ÷ height (in)²
The WHO classifies adult results into four primary categories:
- Under 18.5 — Underweight
- 18.5 – 24.9 — Healthy weight
- 25 – 29.9 — Overweight
- 30 and above — Obese
A worked example
Someone who is 172 cm (5'8") and 74 kg (163 lb): 1.72 squared is 2.958, and 74 ÷ 2.958 = 25.0 — right on the boundary between healthy weight and overweight. For that height, the healthy BMI range corresponds to roughly 55–74 kg (121–162 lb), which the calculator shows automatically.
Why BMI is useful — and where it fails
Across large populations, BMI tracks body fat and disease risk remarkably well: studies following hundreds of thousands of adults show mortality risk rising steadily above a BMI of about 25. That makes it an excellent first-pass screening tool that requires nothing but a scale and a tape measure.
At the individual level it has well-known blind spots. It cannot tell muscle from fat — rugby players and bodybuilders routinely register as obese. It says nothing about fat distribution, even though visceral (abdominal) fat is far more harmful than fat stored on the hips. And it can underestimate risk in older adults, whose muscle loss can hide rising body fat behind a "healthy" number. If your result surprises you, waist-to-height ratio and body composition testing add the missing context.
Common mistakes to avoid
- Measuring height in shoes or weighing yourself at different times of day — both add noise. Measure barefoot, in the morning, before eating.
- Treating one reading as a trend. BMI changes slowly; check it monthly or quarterly rather than daily.
- Chasing a specific BMI decimal. The difference between 24.7 and 25.1 is meaningless for an individual. Aim for the range, not the digit.
- Using adult cutoffs for children. Under-20s require age- and sex-specific percentile charts, which this calculator does not provide.
What to do with your result
If you're above the healthy range and want to bring your BMI down, the proven route is a moderate calorie deficit — our calorie deficit calculator will turn your goal into a daily calorie target and a dated, week-by-week forecast. To see what a healthy weight actually looks like for your height across four clinical formulas, try the ideal weight calculator, and keep your hydration matched to your activity with the water intake calculator.