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MasterMath

BMI Calculator

At 70 kg and 175 cm your BMI is 22.9, inside the healthy range the WHO puts at 18.5 to 25. Work out yours and see the weight range it implies for your height.

Body mass index

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Body mass index—
WHO classification—
Healthy minimum weight—
Healthy maximum weight—
Distance from the range—

How this was worked out

    Indicative result. BMI does not distinguish between fat and muscle, so it misclassifies very muscular people and older people with little lean mass. It is a signal, not a diagnosis.

    The formula

    BMI = weight in kg ÷ (height in metres)²

    Where it comes from

    The body mass index was devised by Adolphe Quetelet in the 1830s as a statistical description of populations, not of individuals. It divides weight by height squared, which makes people of different heights roughly comparable, and it says nothing at all about what that weight is made of.

    How to work it out by hand

    1. Convert your height from centimetres to metres by dividing by 100
    2. Square that number
    3. Divide your weight in kilograms by the result
    4. Compare it against the WHO bands: under 18.5, 18.5 to 25, 25 to 30, over 30

    What is worth knowing

    The famous limitation is real: a muscular athlete and a sedentary person of the same height and weight get the same BMI, and only one of them has a problem. The less discussed limitation cuts the other way — an older person who has lost muscle can sit inside the healthy band while carrying too much fat. That is why waist circumference has become the more useful single number for individual risk: over 94 cm for men and 80 cm for women raises risk regardless of BMI. Use BMI for the direction of travel and something else for the diagnosis.

    Frequently asked questions

    What is a healthy BMI?

    The WHO puts the healthy range at 18.5 to 24.9. Below that is underweight and above it is overweight, with obesity from 30.

    Does BMI work for athletes?

    Poorly. Muscle is denser than fat, so a lean, muscular person often scores as overweight. For them, body fat percentage is the useful measure.

    Does it work for children?

    Not in this form. Children are assessed on age and sex percentile charts, because the healthy range changes as they grow.

    What should I use instead?

    Waist circumference, or the waist-to-height ratio, both of which track abdominal fat. Keeping your waist under half your height is a decent rule of thumb.