BMI Calculator

This blend of weight and height is remarkably sound, considering its simplicity.


The bathroom scale gives most people as much information as they want, thank you very much. Those who want a better fix on their relative body fat have plenty of choices:

Body mass index | Waist-hip ratio | Other measures

Body Mass Index

This blend of weight and height is remarkably sound, considering its simplicity. And because BMI is widely used in studies, it is the only body fat index that conveys risk of disease or death. You need only rudimentary math skills and a calculator. According to the National Institute of Health's 1998 report, a normal BMI is about 18.5 to 25.

Accuracy: Reliable but not foolproof; may peg heavily muscled people as obese
Starting cost: Zero
Convenience: See for yourself...

Enter your weight:

Enter your height:
     feet      inches

Your body mass index is:

Waist-Hip Ratio

Divide your waist size at its smallest by your hip size at its largest and you get a key to how much fat is stored in the abdomen, where it raises the risk of heart disease. The lowest healthy ratio is not yet known. But many experts agree that women with ratios of 0.8 or lower and men with ratios of 1 or lower are in good shape.

Accuracy: Rough
Starting cost: Zero
Convenience: See for yourself...

Enter your waist size:

Enter your hip size:

Your waist-hip ratio is:

Other Measures

Here are some other tests that measure body fat. Sorry, you're on your own for these–no JavaScript calculators included.

Special calipers are used to measure folds of skin and fat in several spots on the body and average them. It is not a precise method; a reading of 25 percent body fat could mean an actual number as high as 28 or as low as 22–or worse with a badly trained technician. Some obesity scientists describe this method as a rip-off or "faux information."

Accuracy: So-so, or worse
Starting cost: $10 to $20
Convenience: Widely available at health clubs; takes a few minutes

You lie down, a technician attaches electrodes to one hand and one foot, and a harmless radio-frequency pulse is run through the body to measure its water content. That number provides a guide to body fat with an error of 2 or 2 1/2 percentage points. But exercise and liquid intake before the test can skew results.

Accuracy: Better than the pinch test
Starting cost: $25
Convenience: Takes only a few minutes; found at health clubs and sports medicine clinics

So far the "gold standard" of body-fat measurement, this test requires you to expel the air from your lungs and get dunked into a pool–half a dozen times. It under- or overestimates body fat by only 1 percentage point.

Accuracy: The best
Starting cost: $25 to $50
Convenience: Available at many hospitals and some gyms, but it is grueling and can last an hour

An egg-shaped chamber that offers precision without pain. You step in, sit for 20 seconds, and that's it. The chamber measures air displacement, which can be converted to relative fat when weight is factored in, since muscular people are denser.

Accuracy: Preliminary tests show it's as good as immersion.
Starting cost: $25 to $125
Convenience: Found at only a few dozen big hospitals and doctor's offices, but it's quick and easy