BMI Calculator
Body Mass Index from your height and weight — with your category and the exact working shown.
How BMI is calculated
Body Mass Index divides your weight by the square of your height. In metric units the formula is simply BMI = weight (kg) ÷ height (m)². Imperial values are converted to metric first, so the result is the same either way.
BMI is a fast, well-established screen for weight relative to height. It doesn't measure body fat directly, so muscle, frame size, and age can shift what the number means for you.
BMI categories (adults)
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
FAQ
What is a healthy BMI range?
For most adults a BMI from 18.5 to 24.9 is classed as a healthy weight. Below that is underweight; 25–29.9 is overweight; 30 or above is obese.
Is BMI accurate for athletes?
Not always. BMI uses only height and weight, so very muscular people can read as overweight even with low body fat. Use it as a quick screen, not a diagnosis.
Does BMI differ for children?
Yes. For under-18s, BMI is read against age-and-sex percentile charts rather than the fixed adult bands above. This tool is intended for adults.