Body Fat Calculator

Estimate your body fat percentage with a tape measure, using the U.S. Navy method. Enter your height and your neck, waist, and (for women) hip measurements; add your weight to see fat and lean mass.

An estimate, not a measurement

The tape-measure method is usually within about 3 to 4 percentage points of lab tests, but it can be further off for some bodies. It isn't meant for people under 18 or during pregnancy. For an accurate measurement, ask a health professional.

Estimated body fat

20.2%

Fat mass: 35.6 lb
Lean mass: 140.4 lb

Results are estimates for information only and do not constitute financial, medical, or legal advice.

How it works

The U.S. Navy developed these equations in 1984 by comparing tape measurements with underwater weighing. They estimate body density from the measurements and convert it to a body fat percentage with the Siri equation.

The formulas (in centimeters)

Men: density = 1.0324 − 0.19077 × log(waist − neck) + 0.15456 × log(height)

Women: density = 1.29579 − 0.35004 × log(waist + hip − neck) + 0.221 × log(height)

Body fat % = 495 ÷ density − 450

Worked example

A man 178 cm (70 in) tall with a 38 cm (15 in) neck and a 90 cm (35.5 in) waist.

Density: 1.0324 − 0.19077 × log(52) + 0.15456 × log(178) ≈ 1.0529.
Body fat: 495 ÷ 1.0529 − 450 ≈ 20.2%.

Sources

Hodgdon JA, Beckett MB.Prediction of Percent Body Fat for U.S. Navy Men from Body Circumferences and Height. Naval Health Research Center, report 84-11, 1984. The equation for women is in the companion report 84-29.

Frequently asked questions

How accurate is the tape-measure method?

In the original Navy study, the equation was within about 3.5 percentage points of underwater weighing for most people. It's quick and free, but it's an estimate: results can be off for very muscular or very lean people, or if the tape isn't placed the same way each time.

How do I measure correctly?

Use a flexible tape that sits flat against the skin without squeezing. Measure the neck just below the larynx, the waist at the navel (men) or at the narrowest point (women), and the hips at the widest point. Take each measurement two or three times and use the average.

What body fat percentage is healthy?

It varies with age, sex, and other factors, and there isn’t one number that fits everyone. If you have questions about your body composition and your health, a health professional can look at the whole picture.