How do I calculate body fat with a tape measure?

Measure height, neck and waist (and hips for women) in inches, then apply the Navy equation. Men: 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76. Women: 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387. The page converts centimetres for you and shows each step.

What is a healthy body fat percentage?

ACE's chart puts 'fitness' at 14–17% for men and 21–24% for women, and 'average' at 18–24% and 25–31%. Below 2–5% for men or 10–13% for women is essential fat, the minimum the body needs, not a target. Healthy ranges also rise somewhat with age.

How accurate is the US Navy body fat method?

For the women's equation the Navy reported a standard error of 3.6 percentage points against underwater weighing, which is how both equations were validated. It is better than BMI at telling muscle from fat and worse than a DEXA scan. Its strength is consistency: the same tape and the same spots, week to week, show the direction of change well.

Where exactly should I measure my waist?

Men at the navel; women at the narrowest point, which is usually a little above the navel. Keep the tape level all the way round, breathe out normally, and don't pull it tight enough to dent the skin.

How does this compare to BMI?

BMI can't distinguish muscle from fat. This method uses circumferences, so a muscular person with a slim waist gets a low body-fat figure even when BMI calls them overweight. The two answer different questions; the BMI and waist-to-hip pages are linked below.

Is this the method the military uses?

These are the Hodgdon-Beckett equations the Navy developed in 1984 and the Department of Defense adopted for its services. The Army moved to a single waist measurement in 2023 (Army Directive 2023-11) with its own equation, which this page does not use.

Body Fat Calculator (US Navy Tape Method)

Body fat percentage from a tape measure by the US Navy equations, with the working in inches, the ACE category, and fat and lean mass.

Inputs

Sex

Height(cm)

50 cm250 cm

Neck(cm)

20 cm60 cm

Waist(cm)

40 cm200 cm

Weight (optional, for fat mass)(kg)

0 kg300 kg

Units

Include CalculateEveryday mark

Body fat

17.0%

Fitness

AthletesFitnessAverageObese

Category (ACE): Fitness (14–17%)
Working (inches): 86.010 × log₁₀(33.5 − 15.0) − 70.041 × log₁₀(68.9) + 36.76 = 17.0
Fat mass: 12.8 kg
Lean mass: 62.2 kg
Method: US Navy (Hodgdon & Beckett, 1984)

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What each Body Fat input means

Neck: Just below the larynx (Adam's apple), with the tape sloping slightly down toward the front. Don't flare the neck or let the tape sink into the skin.
Waist: Men: around the abdomen at the navel. Women: at the narrowest point of the waist, usually above the navel. Measure at the end of a normal breath out, relaxed, not sucked in.
Hip: Women only: around the widest part of the buttocks, feet together. Men's equation doesn't use it.
Height: Barefoot, standing straight. Height enters the equation through a logarithm, so an error of a centimetre or two changes the result only a little.
Weight (optional, for fat mass): Optional. The equations don't need it; it is used only to turn the percentage into kilograms or pounds of fat and lean mass. Set it to 0 to skip.

Body Fat formula

Men: %BF = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76 · Women: %BF = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387 (all in inches)

\%BF_{\text{men}} = 86.010\log_{10}(w - n) - 70.041\log_{10}(h) + 36.76

The US Navy method estimates body fat from a tape measure and a height. James Hodgdon and Marcie Beckett at the Naval Health Research Center fitted the equations in 1984 by measuring sailors' circumferences and comparing them with body fat from underwater weighing; the Department of Defense later adopted them for all the services. Men need the neck and the waist at the navel; women need the neck, the waist at its narrowest and the hips at their widest. The equations take logarithms of those girths and of height, and the coefficients were fitted to measurements in inches, so this page converts centimetres to inches before anything else and shows the working in inches. Fat tends to collect at the waist and hips while the neck tracks frame size, which is why the gap between them carries most of the information. The result is set against the American Council on Exercise categories, and if you add your weight, the page splits it into fat mass and lean mass.

Body Fat worked example

A man 175 cm tall with a 38 cm neck and an 85 cm waist. In inches those are 68.9, 15.0 and 33.5, so waist minus neck is 18.5. Then 86.010 × log₁₀(18.5) = 108.99, minus 70.041 × log₁₀(68.9) = 128.75, plus 36.76, gives 17.0% body fat — the top of ACE's 'fitness' band for men. At 75 kg that is 12.8 kg of fat and 62.2 kg of lean mass.

More Body Fat examples

A woman 165 cm tall with a 32 cm neck, 72 cm waist and 98 cm hips: in inches, waist plus hip minus neck is 54.3 and height is 65.0. The women's equation gives 27.7%, in ACE's 'average' band of 25–31%, which at 62 kg is 17.2 kg of fat.

A man 5 ft 10 in (70 in) with a 15.5 in neck and a 36 in waist, weighing 190 lb: 86.010 × log₁₀(20.5) − 70.041 × log₁₀(70) + 36.76 = 20.4%, which is 38.7 lb of fat and 151.3 lb of lean mass.

Where the Body Fat calculator can give the wrong answer

Until 2 October 2026 this page put centimetres into the inch equations, which read about 6 points too high for men and far more for women. If you saved a figure from before then, recalculate it; the method itself has not changed.
Hodgdon and Beckett reported a standard error of 3.6 percentage points for the women's equation against underwater weighing, so a result of 22% means roughly 18–26% for one person. DEXA or hydrostatic weighing is more precise.
Tape placement is the biggest source of error. A waist measured after a meal, or with the stomach held in, can move the answer by several points; measure the same way at the same time of day to track a trend.
The equations assume an ordinary fat distribution. A very muscular neck lowers the estimate, and fat carried mostly on the thighs is invisible to the men's formula.
Results outside 2–60% are refused rather than shown, because they come from mis-entered measurements, not real bodies. The men's formula also needs the waist to be larger than the neck.

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Body Fat reference table

American Council on Exercise body-fat categories
Category	Women	Men
Essential fat	10–13%	2–5%
Athletes	14–20%	6–13%
Fitness	21–24%	14–17%
Average	25–31%	18–24%
Obese	32% and over	25% and over

Source: American Council on Exercise (ACE), body composition chart

Body Fat FAQ

: Measure height, neck and waist (and hips for women) in inches, then apply the Navy equation. Men: 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76. Women: 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387. The page converts centimetres for you and shows each step.
: ACE's chart puts 'fitness' at 14–17% for men and 21–24% for women, and 'average' at 18–24% and 25–31%. Below 2–5% for men or 10–13% for women is essential fat, the minimum the body needs, not a target. Healthy ranges also rise somewhat with age.
: For the women's equation the Navy reported a standard error of 3.6 percentage points against underwater weighing, which is how both equations were validated. It is better than BMI at telling muscle from fat and worse than a DEXA scan. Its strength is consistency: the same tape and the same spots, week to week, show the direction of change well.
: Men at the navel; women at the narrowest point, which is usually a little above the navel. Keep the tape level all the way round, breathe out normally, and don't pull it tight enough to dent the skin.
: BMI can't distinguish muscle from fat. This method uses circumferences, so a muscular person with a slim waist gets a low body-fat figure even when BMI calls them overweight. The two answer different questions; the BMI and waist-to-hip pages are linked below.
: These are the Hodgdon-Beckett equations the Navy developed in 1984 and the Department of Defense adopted for its services. The Army moved to a single waist measurement in 2023 (Army Directive 2023-11) with its own equation, which this page does not use.