BMI Calculator

How BMI is calculated

Body mass index relates your weight to your height to give a quick screening measure of body size. The calculator accepts metric or imperial units — feet, inches, pounds, and ounces are converted to meters and kilograms first — and also shows what you would weigh at a target BMI of your choice.

Formula

BMI = weight (kg) ÷ height (m)²

Weight at target BMI = target × height (m)²

Worked example

At 75 kg and 180 cm: height is 1.80 m, so BMI = 75 ÷ (1.80 × 1.80) = 75 ÷ 3.24 = 23.1 — inside the healthy range. To reach a target BMI of 22, the weight would be 22 × 3.24 = 71.3 kg.

BMI categories (adults)

Where BMI falls short

Because BMI only uses height and weight, it can misclassify people whose body composition is unusual. A muscular athlete may land in the "overweight" range despite low body fat, while an older adult who has lost muscle can read as "healthy" while carrying excess fat. BMI cut-offs were derived largely from adult populations of European descent and fit less well for other groups — some health bodies use a lower overweight threshold (around 23) for people of South Asian heritage. It also does not apply to children and teens, who need age- and sex-specific percentile charts.

Measurements that add context

Pair BMI with a waist measurement — carrying fat around the middle raises health risk independently of BMI, and a waist over about 94 cm (37 in) for men or 80 cm (31.5 in) for women is a common warning line. Waist-to-height ratio (keeping your waist under half your height) is another quick check. Trends over time matter more than a single reading, so track the direction of change rather than fixating on one number.

BMI is a screening tool, not a diagnosis — it cannot tell muscle from fat. For energy needs, pair it with the BMR calculator and the calorie calculator.