Body Fat Calculator: U.S. Navy Method

Estimate your body fat percentage with nothing more than a tape measure, using the circumference equations the U.S. Navy developed and validated against underwater weighing. Add your weight to see your fat mass and lean mass.

By the FitStack team. Last updated October 18, 2026. Formulas and sources are listed on this page.

How to measure

Get set up. Use a flexible, non-stretch tape. Measure in the morning before eating, standing relaxed with feet together, on bare skin.
Measure your height. Stand barefoot against a wall, heels together, looking straight ahead. Record to the nearest half inch or centimetre.
Measure your neck. Wrap the tape just below the larynx (Adam's apple), sloping slightly down toward the front. Keep it snug without compressing the skin and keep your shoulders down.
Measure your waist. Men: horizontally at the level of the navel. Women: at the narrowest point of the abdomen. Measure at the end of a normal breath out, without pulling the stomach in.
Measure your hips (women). Standing with feet together, measure horizontally around the widest part of the buttocks.
Repeat and average. Take each measurement three times and enter the average. Use the same tape, time of day and spots each time you re-measure.

The Navy body fat equations

Measurements in inches; log10 is the base-10 logarithm.

Men: body fat % = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76 Women: body fat % = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387

Hodgdon and Beckett at the Naval Health Research Center derived these equations in 1984 from 602 men and a separate group of women, with body fat measured by underwater weighing; the men's equation correlated 0.90 with the lab result in a cross-validation group.¹ The U.S. military used them for decades in its body composition program.² Metric measurements are converted to inches before calculating.

Worked example

A man, 70 in (178 cm) tall, neck 15.5 in, waist 36 in:

86.010 × log10(36 − 15.5) − 70.041 × log10(70) + 36.76 = 86.010 × 1.312 − 70.041 × 1.845 + 36.76 ≈ 20.4%

Body fat categories

Category	Men	Women
Essential fat	2 to 5%	10 to 13%
Athletes	6 to 13%	14 to 20%
Fitness	14 to 17%	21 to 24%
Average	18 to 24%	25 to 31%
Obese	25% and above	32% and above

Ranges from the American Council on Exercise.³ They describe adults in general and don't adjust for age.

Limits of tape measurements

Expect an error of roughly 3 to 4 percentage points compared with a lab method.
Very muscular people with thick necks can get a reading that is too low; people who carry fat mainly on the hips and thighs can get one that is off in either direction.
It is not designed for pregnancy, children or teenagers.

Your lean mass makes the TDEE calculator more accurate: enter your body fat there and it switches to the Katch-McArdle equation.⁴ The protein calculator then sets the intake that helps you keep that lean mass.

Frequently asked questions

How accurate is the Navy body fat method?

In the original Navy studies the equations correlated well with underwater weighing, and tape estimates typically land within about 3 to 4 percentage points of a lab measurement for most people. They are less accurate for very lean or very muscular people and for people with an unusual fat distribution. The biggest source of error is inconsistent measuring, so the trend over time is more useful than any single reading.

What is a healthy body fat percentage?

Using the American Council on Exercise ranges, roughly 14 to 24% for men and 21 to 31% for women covers the fitness and average categories. Essential fat, the minimum for normal body function, is about 2 to 5% for men and 10 to 13% for women. Health risk rises in the obese range: 25% and above for men, 32% and above for women.

Why does my smart scale give a different number?

Bioelectrical impedance scales estimate body fat from how a small current passes through your legs, which is strongly affected by hydration, recent meals and exercise. They can differ from tape methods by several points on the same day. Pick one method, measure under the same conditions each time and follow the trend.

How does the Navy method compare with DEXA?

DEXA scans are among the most accurate practical methods and also show where fat and lean mass sit, but they cost money and use a small dose of radiation. The Navy tape method is free and repeatable at home, at the cost of a wider error. Many people use a DEXA scan occasionally and the tape method in between.

How often should I measure my body fat?

Every four weeks is enough. Body fat changes slowly, and month-to-month changes smaller than about one percentage point are within the error of the method.