BMI Calculator

What BMI Measures

Body Mass Index (BMI) is a single number that compares your weight to your height. The idea is simple: a taller person is expected to weigh more, so instead of looking at weight alone, BMI divides your weight by your height squared. That puts people of different heights on the same scale, which is why doctors and health surveys use it as a quick screening number.

The scale under the calculator shows where a BMI sits among the standard adult categories - underweight, normal, overweight, and obese. The marker moves as you change your height or weight.

This is an educational tool, not medical advice. BMI is a rough screening number. It does not measure body fat directly and does not account for muscle, build, age, sex, or where weight is carried - so a muscular athlete can read as “overweight.” The adult categories below do not apply to children or teens (who use age-and-sex percentiles). For anything about your health, talk to a doctor. See our disclaimer.

The Formula

$$\text{BMI} = \frac{\text{weight (kg)}}{\text{height (m)}^2}$$

In imperial units it is $\text{BMI} = 703 \times \dfrac{\text{weight (lb)}}{\text{height (in)}^2}$ - the 703 just converts pounds and inches into the metric result.

How to Use It

1. Choose metric (cm, kg) or imperial (ft/in, lb).
2. Enter your height and weight.
3. Read your BMI and its category.

Adult BMI Categories

BMI range	Category
Below 18.5	Underweight
18.5 - 24.9	Normal weight
25.0 - 29.9	Overweight
30.0 and above	Obese

Worked Example

For a 170 cm, 65 kg adult: height is 1.70 m, so $1.70^2 = 2.89$, and $65 \div 2.89 \approx 22.5$ - a BMI of 22.5, in the normal range.