BMI Calculator
This calculator is for informational purposes only and is not a substitute for professional medical advice. Consult a healthcare provider for personal health decisions.
BMI = weight (kg) ÷ height (m)²
How BMI Is Calculated
Body Mass Index (BMI) is a simple ratio of weight to height squared, used worldwide as a screening tool for weight categories. The formula is: BMI = weight (kg) ÷ height (m)². If you measure height in centimeters, convert to meters first by dividing by 100. BMI does not directly measure body fat, but it correlates reasonably well with body composition for most adults and helps flag potential health risks associated with very low or very high weight.
Consider a person who weighs 70 kg and stands 175 cm tall. Convert height to meters: 175 ÷ 100 = 1.75 m. Square it: 1.75² = 3.0625. Divide weight by that value: 70 ÷ 3.0625 = 22.86, which rounds to 22.9. According to standard WHO adult categories, a BMI below 18.5 is underweight, 18.5–24.9 is normal, 25.0–29.9 is overweight, and 30.0 or above is obese. A BMI of 22.9 falls comfortably in the normal range.
For imperial units, the equivalent formula is: BMI = (weight in pounds ÷ height in inches²) × 703. A person weighing 154 lb (70 kg) and 69 inches tall (175 cm) would compute (154 ÷ 69²) × 703 = (154 ÷ 4,761) × 703 ≈ 22.9 — the same result. Always use consistent units within a single calculation; mixing pounds with centimeters without conversion will produce nonsense.
BMI has well-known limitations. It does not distinguish muscle from fat, so athletes with high muscle mass may be classified as overweight despite low body fat. It also tends to underestimate health risk in older adults who have lost muscle mass. BMI ranges for children and teens use age- and sex-specific percentiles rather than fixed adult cutoffs. Despite these caveats, BMI remains a useful first-pass screening number because it is easy to compute and widely understood by clinicians.
Use this calculator to check your current BMI, track changes over time as you adjust diet or exercise, or estimate a target weight for a desired BMI at your height. Enter your weight and height in whichever units you prefer — the calculator handles metric and imperial conversions internally and returns your BMI value plus the corresponding category label.
Examples
| Example | Result |
|---|---|
| 70 kg, 175 cm | BMI 22.9 — Normal |
| 60 kg, 165 cm | BMI 22.0 — Normal |
| 90 kg, 180 cm | BMI 27.8 — Overweight |
| 55 kg, 170 cm | BMI 19.0 — Normal |
| 100 kg, 175 cm | BMI 32.7 — Obese |
| 45 kg, 160 cm | BMI 17.6 — Underweight |
| 80 kg, 190 cm | BMI 22.2 — Normal |
| 65 kg, 150 cm | BMI 28.9 — Overweight |
Frequently asked questions
For most adults, a BMI between 18.5 and 24.9 is considered normal. Below 18.5 is underweight; 25–29.9 is overweight; 30 and above is obese.
BMI can overestimate body fat in very muscular individuals because muscle weighs more than fat per unit volume. Athletes may benefit from additional body composition tests.
Divide centimeters by 100. For example, 175 cm = 1.75 m. Then square the result before dividing weight into it.