How is BMI calculated?

Weight in kilograms divided by height in metres squared. Someone 1.75 m and 70 kg has a BMI of 22.9. Imperial entries are converted first, so both unit systems give the same figure.

What do the categories mean?

Below 18.5 is underweight, 18.5 to 25 is the healthy band, 25 to 30 is overweight, and 30 or above is obese. These are the WHO figures for adults.

Why does BMI call a muscular person overweight?

Because it uses only height and weight, and cannot tell muscle from fat. Muscle is denser, so athletes often read as overweight while carrying very little fat.

Does BMI work for everyone?

No. It does not apply to children or teenagers, who need age and sex percentiles, nor during pregnancy. The cut-offs also differ by population: basic mode uses the standard WHO adult figures, and advanced mode can switch to the lower Asian action points of 23 and 27.5, or the Indian consensus figures of 23 and 25.

How is body fat percentage estimated?

Two ways, shown side by side. The US Navy method uses your height, waist and neck — plus hips for women — and is the better of the two because it measures where fat actually sits. The Deurenberg method needs no tape measure but is calculated from your BMI and age, so it inherits BMI's inability to tell muscle from fat. They will disagree, and that gap is informative.

How accurate are these body fat and calorie figures?

They are estimates from formulas fitted on particular groups of people, not measurements of you. A tape-measure body fat estimate is typically within 3 to 5 percentage points of a DEXA scan, and where you place the tape is the largest source of error. Calorie needs vary by 10 percent or more between people of identical size.

BMI Calculator: Body Mass Index in kg or lb

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Height (cm)

Weight (kg)

22.9Healthy weight

Healthy weight for this height: 56.7–76.6 kg

BMI is a screening figure, not a diagnosis, and it cannot tell muscle from fat. Talk to a doctor about what it means for you.

Common questions

How is BMI calculated?
Weight in kilograms divided by height in metres squared. Someone 1.75 m and 70 kg has a BMI of 22.9. Imperial entries are converted first, so both unit systems give the same figure.
What do the categories mean?
Below 18.5 is underweight, 18.5 to 25 is the healthy band, 25 to 30 is overweight, and 30 or above is obese. These are the WHO figures for adults.
Why does BMI call a muscular person overweight?
Because it uses only height and weight, and cannot tell muscle from fat. Muscle is denser, so athletes often read as overweight while carrying very little fat.
Does BMI work for everyone?
No. It does not apply to children or teenagers, who need age and sex percentiles, nor during pregnancy. The cut-offs also differ by population: basic mode uses the standard WHO adult figures, and advanced mode can switch to the lower Asian action points of 23 and 27.5, or the Indian consensus figures of 23 and 25.
How is body fat percentage estimated?
Two ways, shown side by side. The US Navy method uses your height, waist and neck — plus hips for women — and is the better of the two because it measures where fat actually sits. The Deurenberg method needs no tape measure but is calculated from your BMI and age, so it inherits BMI's inability to tell muscle from fat. They will disagree, and that gap is informative.
How accurate are these body fat and calorie figures?
They are estimates from formulas fitted on particular groups of people, not measurements of you. A tape-measure body fat estimate is typically within 3 to 5 percentage points of a DEXA scan, and where you place the tape is the largest source of error. Calorie needs vary by 10 percent or more between people of identical size.

Tools

BMI calculator