ToolWrenBody Mass Index (BMI) is a quick screening number that relates your weight to your height. It is widely used because it needs only two measurements, but it has real limitations. Here is how to calculate it and how to interpret it sensibly.
The formula
Metric: BMI = weight(kg) ÷ height(m)². So an 80 kg person who is 1.80 m tall has a BMI of 80 ÷ (1.80 × 1.80) = 80 ÷ 3.24 ≈ 24.7.
Imperial: BMI = 703 × weight(lb) ÷ height(in)². Our BMI calculator does both for you and shows your category instantly.
The categories
The standard adult ranges are: under 18.5 = underweight, 18.5–24.9 = healthy weight, 25–29.9 = overweight, and 30+ = obese. These thresholds are the same regardless of age or sex for adults.
What BMI doesn't tell you
BMI cannot distinguish muscle from fat, so very muscular people can score as 'overweight' while being lean. It also ignores fat distribution and does not apply directly to children, pregnant people or the elderly. For a fuller picture, combine it with a body-fat estimate.
Going further
If you are planning changes to diet or activity, BMI is just a starting point. Estimate your daily energy needs with the BMR calculator and see how exercise adds up with the calories-burned calculator. Always talk to a healthcare professional for personal advice.