Body Fat Calculator: the US Navy Tape Method

Body fat percentage ranges

These are the general ranges the American Council on Exercise (ACE) publishes. They describe where most people in each group fall. They are not health targets or a grade, and a tape measure cannot tell you anything about your health on its own.

ACE's own name for the last band is "obese"; we call it "higher" because a circumference estimate is not a diagnosis. Women carry about 8 to 10 points more essential fat than men, mostly in breast tissue, the hips and around the reproductive organs, which is why every band sits higher for women. Essential fat is the minimum the body needs for hormones, nerves and organ function. Living at or below it is not a fitness goal; competitive bodybuilders only touch it for a day or two, and many women lose their periods well before they get there.

How the Navy formula works

The equations come from Hodgdon and Beckett at the Naval Health Research Center, who published them in 1984 after measuring Navy men and women and checking the results against underwater weighing. Their reports predicted body density from centimeters; the Department of Defense rewrote them to give body fat percent straight from inches in its body composition instruction (DoDI 1308.3, 2002), and that is the version below and in the calculator. All measurements go in as inches.

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

The idea is simple. Fat collects around the waist (and, for women, the hips), while the neck tracks frame size and muscle. A bigger waist relative to the neck means more fat; a taller body spreads the same waist over more frame, so height pulls the number down.

Worked example, man: 5 ft 10 in (70 in, 178 cm), 180 lb (82 kg), neck 15.5 in (39.4 cm), waist at the navel 34 in (86.4 cm).

Worked example, woman: 5 ft 5 in (65 in, 165 cm), 150 lb (68 kg), neck 13 in, waist 29 in, hips 39 in. Waist plus hips minus neck is 55. Then 163.205 × log10(55) = 284.04, and 97.684 × log10(65) = 177.09. So 284.04 − 177.09 − 78.387 = 28.6%, about 42.8 lb (19.4 kg) of fat mass and 107.2 lb (48.6 kg) of lean mass.

If you measure in centimeters, convert to inches first (divide by 2.54), as the calculator does. Plugging centimeters straight into the inch equations is a real and common slip: it adds about 6.5 points for a man and about 26.5 for a woman, whatever the measurements.

How to measure: exact tape positions

The formula is only as good as the tape. Use a soft, non-stretch tape, measure on bare skin, and keep the tape level all the way around (a mirror or a second person helps). Round to the nearest half inch or centimeter.

• Height. Barefoot, heels against a wall, looking straight ahead. Mark the top of your head with a book held flat against the wall.
• Neck. Just below the larynx (the Adam's apple), with the tape sloping slightly down toward the front. Look straight ahead and keep your shoulders down; do not flare your neck.
• Men's waist. Horizontally around the abdomen at the level of the navel, at the end of a normal breath out. No sucking in.
• Women's waist. Around the natural waist at its narrowest point, usually a little above the navel, at the end of a normal breath out.
• Women's hips. Around the widest part of the glutes, seen from the side, feet together.

Take each measurement three times and average them. Measure at the same time of day, ideally on waking and before food or water: a large meal or a salty dinner can add half an inch to the waist by itself. For tracking, once every two to four weeks is plenty.

What changes the answer

Small tape errors move the result more than most people expect. Starting from the worked examples above:

The waist is the big lever, so it is where care pays off. A tape pulled tight, a held breath or a measurement an inch above the navel can each be worth two points for a man. Weight does not enter the formula at all; it only splits the percentage into pounds of fat and lean mass.

That also explains the method's blind spots. A lifter with a thick, trained neck reads leaner than they are. Someone who carries fat on the thighs and arms rather than the midsection can read leaner too, while a man with a broad, muscular trunk can read higher. Bloating, water retention around the menstrual cycle, and posture all show up as waist inches.

How accurate is it?

Validation work done for the Department of Defense puts the standard error of circumference equations like these at roughly 3.5 percentage points for men and 3.6 for women. In plain terms: if the calculator says 20%, your real number is most likely somewhere between about 16 and 24%. Later studies comparing the tape against DEXA scans land in the same place, roughly 3 to 4 points either way for most adults, with bigger misses at the very lean and very high ends.

Every method is an estimate; even DEXA has its own error. So do not compare numbers from different methods, and do not chase a decimal point. What the tape does well is consistency: the same person, same tape, same spots, same time of day will show real change over weeks. A waist that drops an inch while your lifts hold or climb means more than any single percentage.

How to use the number

Track the trend, not the reading. Measure every two to four weeks and look at the direction over two or three months. A drop of one or two points over a couple of months is real progress; a jump of two points in a week is water, food or tape position.

• Losing fat. Aim to lose about 0.5 to 1% of bodyweight a week, from a deficit of no more than about 500 calories a day. Our calorie calculator sets that up, and the guide to cutting without losing muscle keeps the lean mass on your side of the ledger. Women should not go below about 1,200 calories a day, or men 1,500, without a doctor involved.
• Building muscle. Watch lean mass and the waist together. If weight climbs, lean mass climbs, and the waist barely moves, the gain is going where you want. How to build muscle as a woman covers why the scale is a poor judge here.
• Doing both. Newer lifters and people returning after a break can lose fat and gain muscle at the same time. The scale may not move, which is exactly when the tape is useful. The body recomposition guide shows how to set it up.
• Setting protein. If you carry a lot of body fat, base protein on goal weight or lean mass rather than total weight. The protein calculator does the math, and how much protein you need explains the numbers behind it.

If you want calories, protein, carbs and fat set together, the macro calculator takes it from there.

Questions people ask

How accurate is the Navy body fat calculator?

Within about 3 to 4 percentage points for most adults, compared with underwater weighing and DEXA. It is most reliable for tracking change in the same person over time.

Why does a woman's version use the hips?

Women store more fat around the hips and thighs, so the waist alone misses much of it. Adding the hip measurement made the women's equation fit the lab results far better.

Why did my body fat go up when I gained muscle?

The formula only sees circumferences. If your neck stayed the same and your waist grew a little from a thicker trunk, food or water, the estimate rises. Re-measure on a normal morning and look at the trend over a month.

What is a good body fat percentage?

There is no single good number. Most active women sit somewhere in the 20s and most active men in the teens, and plenty of healthy people sit above that. Pick a direction that supports how you want to train and feel, not a figure from a chart.

Is the Navy method better than a smart scale?

For tracking, usually yes. Bioimpedance scales move with hydration, so a glass of water or a workout can shift them. A tape measured carefully under the same conditions is steadier.

Does the military still use this formula?

These equations were the DoD standard for decades. The services have since been allowed to adopt other approved methods, so check your own branch's current rules if a test counts for you.

Where these numbers come from

The equations are from Hodgdon and Beckett, Prediction of percent body fat for U.S. Navy men and women from body circumferences and height (Naval Health Research Center reports 84-11 and 84-29, 1984), as written in inch form into Department of Defense Instruction 1308.3, DoD Physical Fitness and Body Fat Programs Procedures (2002), which also sets out the measurement sites. The error figures come from Hodgdon and Friedl's 1999 Naval Health Research Center review for the Department of Defense (Technical Document 99-2B). The general ranges are the American Council on Exercise's body fat percentage chart. The sensitivity table and worked examples are our own arithmetic using those equations.

This calculator is for training and general information only. If you have concerns about your weight, eating or health, talk to your doctor.