∑ Calculivo

BMI Calculator

Calculate your Body Mass Index in metric or imperial units.

Unit

Result —

About this calculator

Body Mass Index, or BMI, is a quick screening number that compares your weight to your height. It’s not a perfect measure of health — it doesn’t distinguish between fat and muscle — but it’s widely used by clinicians and public health agencies as a starting point for a conversation about weight.

How it works

In metric units BMI is your weight in kilograms divided by the square of your height in metres. In imperial units the same idea is expressed as weight in pounds divided by the square of height in inches, multiplied by 703 to make the numbers comparable.

Once calculated, the World Health Organization places adults into four broad categories: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, and 30 or above obese. The bands are the same regardless of unit system.

BMI is most accurate for the general adult population. It can mislead for athletes with high muscle mass (who often register as overweight) and for the elderly (who may register as normal but have low muscle mass).

BMI doesn’t replace a clinical assessment. Waist circumference, body composition, blood pressure and lifestyle factors all matter. Treat your BMI number as one signal among many.

Formula

Metric:    BMI = kg / (m × m)
Imperial: BMI = (lb / (in × in)) × 703

Examples

70 kg at 175 cm

A 70-kg adult at 1.75 m has a BMI of 22.9, comfortably inside the normal range.

Result: BMI 22.9 — Normal

180 lb at 68 in

An adult weighing 180 lb at 68 inches has a BMI of 27.4, in the overweight range.

Result: BMI 27.4 — Overweight

Frequently asked questions

Is BMI a good measure of health? +
It’s a useful screening number for populations but a blunt instrument for individuals. Athletes and very muscular people often score above the normal range despite being healthy.
What are the BMI categories? +
Underweight: under 18.5. Normal: 18.5–24.9. Overweight: 25–29.9. Obese: 30 and above. These are the WHO bands used worldwide for adults.
Does BMI apply to children? +
No — children use age- and sex-specific percentiles, not the adult BMI thresholds. Ask a paediatrician for an interpretation.
Should pregnant or athletic adults use BMI? +
Both groups are common exceptions. Pregnancy adds non-fat weight; athletic builds carry extra muscle. Use BMI as one signal alongside body composition.
Why is 703 used in the imperial formula? +
It’s a unit-conversion constant that lets the imperial formula return the same BMI value as the metric one. It removes the need to convert pounds and inches into kilograms and metres.

Related calculators