You can calculate your BMI in 30 seconds with two pieces of information: your weight and your height. The formula has not changed in nearly 200 years, and it is the same one used by the US Centers for Disease Control and the World Health Organization. Here is exactly how to do it.
The formula
BMI equals your weight in kilograms divided by your height in meters squared (kg ÷ m²). For example, a 70 kg adult who is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. That is the entire calculation.
If you measure in pounds and inches, multiply pounds by 703 and divide by inches squared. The result is the same.
What the number tells you
BMI sorts adults into four buckets: under 18.5 is underweight, 18.5–24.9 is normal weight, 25.0–29.9 is overweight, and 30.0 and above is obese. The cutoffs were chosen because population-level health risk rises noticeably at the boundaries.
BMI does not measure body fat directly. It is a screening number — fast, cheap, and useful enough to flag people who would benefit from a closer look at their weight-related health risk.
Common mistakes
Forgetting to square the height. The formula is m², not m. Squaring is the most common error people make on a calculator.
Mixing units mid-formula (e.g. kg with inches). Stick to metric or stick to imperial — do not blend.
Using your height with shoes on, or your weight with a heavy meal in your stomach. Measure consistently.
Track it, do not just calculate it once
One BMI reading is a snapshot. The value comes from tracking the same number over weeks and months and watching for trends. A small drop within the overweight range is meaningful — research shows 5 to 10% body weight loss measurably improves blood pressure, blood sugar, and cholesterol.
Try the free BMI Calculator
Free, offline, available in 20 languages on Android and iOS. 30 seconds is all it takes.
Google Play App StoreA free BMI calculator app removes the friction so you check it consistently. Our BMI Calculator works offline, supports both metric and imperial units, and shows your category instantly.
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