Math

BMI calculator.

Your body mass index and category — in imperial or metric.

BMI is a quick screening tool, not a diagnosis. It doesn't distinguish muscle from fat or account for age, sex or body composition — treat it as a rough guide and talk to a clinician about what's healthy for you.

What BMI measures

Body mass index is weight divided by height squared — in metric it's kilograms ÷ metres², and in imperial it's pounds ÷ inches² × 703, which is just the same formula with a unit-conversion factor folded in. The standard adult categories are: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, and 30 or above obesity. Because BMI uses only height and weight, it can over-state body fat for very muscular people and under-state it for others, and it isn't meant for children, who use age-and-sex percentile charts instead. It's best read as a population-level screening number, not a verdict on an individual's health. To convert between units yourself, the unit converter handles weight and length.

FAQ

How is BMI calculated?
BMI is weight divided by height squared: kg ÷ m² in metric, or lb ÷ in² × 703 in imperial. A 178 cm, 77 kg adult has a BMI of about 24.3.
What is a healthy BMI range?
For adults, 18.5 to 24.9 is classed as normal weight. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obesity. BMI is a screening guide, not a diagnosis.

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