🩺 BMI Calculator
BMI = weight (kg) ÷ height (m)², a 70 kg person at 175 cm has a BMI of 22.9. Enter your values below, results update instantly, entirely on your device.
70 ÷ 1.75² — WHO adult scale
How the bmi calculator works
BMI = weight in kilograms ÷ (height in meters)². WHO adult ranges: under 18.5 underweight · 18.5-24.9 normal · 25-29.9 overweight · 30+ obesity. The units must match the formula: use kilograms and metres, not centimetres, so 175 cm becomes 1.75 m and squares to about 3.06.
Example: 70 kg at 175 cm → 70 ÷ 1.75² = 22.9 (normal range).
BMI is a population screening measure, not a diagnosis: it cannot distinguish muscle from fat, so athletes often read "overweight" while lean-mass poor individuals can read "normal". Health data is exactly the kind of input you shouldn’t hand to random web servers. This calculator never transmits yours anywhere.
Frequently asked questions
What is a healthy BMI?
For adults, the WHO defines the normal range as 18.5-24.9. The calculator also shows the weight range that corresponds to normal BMI at your height.
Is BMI accurate for athletes?
Not particularly, muscle is denser than fat, so muscular people often score 25+ while being very lean. Waist measurements and body-fat percentage are better signals in that case.
Does the formula differ for imperial units?
The imperial form is weight (lb) ÷ height (in)² × 703. Convert first with the lbs-to-kg tool if needed; both routes give the same BMI.
What are the standard BMI categories?
For adults the WHO ranges are: under 18.5 underweight, 18.5-24.9 healthy weight, 25-29.9 overweight, and 30 or above obese. These are population guides, not a diagnosis.
Why can BMI be misleading?
BMI only uses height and weight, so it can't tell muscle from fat or account for frame size, age or body-fat distribution. A muscular athlete may read "overweight" while being lean, treat it as a rough screen, not a health verdict.
How do I calculate BMI step by step?
Convert height to metres, square it, then divide weight in kilograms by the result. For 80 kg at 180 cm: 1.80² = 3.24, and 80 ÷ 3.24 = 24.7, near the top of the normal range.
Does BMI work the same way for children?
No, for children and teens the same weight-over-height² figure is compared against age- and sex-specific percentile charts rather than the fixed adult cut-offs, so the adult categories should not be applied to a child.
Is this bmi calculator accurate and private?
Yes. It uses the standard published formula, shows its working under every result, and computes locally in your browser, your inputs are never sent to a server, and the page works offline.