Body Mass Index (BMI) estimates whether your weight is in a healthy range for your height. It's calculated by dividing your weight in kilograms by the square of your height in metres:
BMI = weight (kg) ÷ height (m)²
In imperial units, BMI = 703 × weight (lb) ÷ height (in)². The calculator above handles both unit systems for you.
| BMI range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
Divide your weight in kilograms by your height in metres squared. For example, 70 kg ÷ (1.75 m × 1.75 m) = 22.9. The calculator above does this in metric or imperial units.
A BMI between 18.5 and 24.9 is considered normal weight. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above falls into the obesity range.
BMI is a useful general screen but doesn't distinguish muscle from fat. Very muscular people may register as overweight, while BMI can underestimate fat in older adults. Pair it with waist-to-hip ratio or body fat percentage for a fuller picture.
The BMI formula and categories are the same for adult men and women. Body composition differs between sexes, which is why BMI is best used alongside other measures rather than on its own.