BMI Calculator

About Body Mass Index (BMI)

Body Mass Index (BMI) is a simple screening measure that uses your height and weight to estimate whether your weight falls within a healthy range. It's widely used by doctors and public health organizations because it's quick to calculate and doesn't require any special equipment, but it's only a general indicator — it doesn't directly measure body fat percentage or account for factors like muscle mass, bone density, age, or sex.

How BMI is calculated

BMI is calculated by dividing your weight in kilograms by the square of your height in meters (BMI = weight (kg) / height (m)²). For example, someone who is 170 cm tall and weighs 65 kg has a BMI of 65 / (1.7 × 1.7) ≈ 22.5, which falls in the normal weight range.

BMI weight categories

The World Health Organization (WHO) classifies adult BMI into four main categories: under 18.5 is underweight, 18.5–24.9 is normal weight, 25–29.9 is overweight, and 30 or above is obese. These thresholds apply to the general adult population and may not be appropriate for children, pregnant women, or highly muscular individuals.

Frequently asked questions

Is BMI an accurate measure of health?

BMI is a useful screening tool at the population level, but it doesn't distinguish between muscle and fat. A very muscular person can have a high BMI without excess body fat, so it should be considered alongside other measures like waist circumference or body fat percentage.

Does BMI apply to children or pregnant women?

No. Children and teenagers need age- and sex-specific growth charts instead of the adult BMI scale, and pregnant women's weight naturally increases in ways the standard BMI categories don't account for.

What should I do if my BMI is outside the normal range?

A BMI outside the normal range doesn't automatically mean a health problem. It's best treated as a starting point for a conversation with a healthcare professional, who can consider your full health picture rather than a single number.