Body fat percentage from a tape measure by the US Navy method, in cm or inches
Runs in your browser. Nothing you type is sent anywhere. Updated on 24 Oct 2026.Body Fat Calculator uses the US Navy circumference equations from DoD Instruction 1308.3. A man of 70 inches with a 36-inch waist and 15-inch neck reads 21.3%, in the ACE acceptable band of 18 to 24%. The method's standard error is about 3.5 percentage points either way.
Choose cm or ft and in under Units, then pick your Sex.
Enter your Height, Waist and Neck; women also measure Hips, widest.
Measure the waist at the navel for men and at the narrowest point for women, as the field label says.
Read the Estimated body fat, its Category and the Likely range, and compare with The ACE categories; Share result copies a link.
This page estimates body fat from a tape measure, using the US Navy circumference method. The equations were fitted by Hodgdon and Beckett at the Naval Health Research Center in 1984 against underwater weighing, and they are the ones written into Department of Defense Instruction 1308.3. Men need height, neck and waist at the navel. Women need height, neck, waist at its narrowest point and hips at the widest point of the buttocks.
The formula works in inches, so centimetres are converted at exactly 2.54 before anything else happens. There is one set of equations, not a separate metric version that could give a slightly different answer.
The result is placed in a category from the American Council on Exercise norms: essential fat, athletes, fitness, acceptable and obesity. The lines differ by sex because women carry more essential fat: acceptable runs from 18 to 24% for men and from 25 to 31% for women. ACE publishes whole-number ranges, so the category is chosen on the reading rounded to a whole number, which is also how the DoD instruction says the result should be reported.
Be clear about the error. The validation figures quoted for these equations give a standard error of about 3.5 percentage points, which means a reading of 22% is somewhere between roughly 18.5% and 25.5% for about two people in three. A tape pulled tight, placed a few centimetres off, or read after breathing in can move the answer by more than that. Measure three times and use the average.
What the tool does not do: it does not measure fat directly, it was fitted on military adults rather than children, older people or athletes at the extremes, and it gives nonsense for readings pushed outside its sample, which the page flags. A DEXA scan or underwater weighing is far more accurate if a precise figure matters. This is general information, not medical advice.
The measurements you enter stay in your browser.
The method uses a tape measure and two equations from DoD Instruction 1308.3. Men enter height, neck and waist at the navel; women add hips. For a man, 86.010 times log10 of waist minus neck, less 70.041 times log10 of height, plus 36.76 gives body fat percentage, all in inches.
Validation figures for the equations give a standard error of about 3.5 percentage points against underwater weighing. A reading of 22% therefore means roughly 18.5% to 25.5% for about two people in three, before any error in measuring. A DEXA scan is considerably more precise when an exact figure matters.
Following DoD Instruction 1308.3: the neck just below the Adam's apple, with the tape as close to horizontal as the neck allows. Men measure the waist at the navel after a normal breath out. Women measure the waist at its narrowest point and the hips at the widest part of the buttocks. Keep the tape level and snug, never compressing the skin.
American Council on Exercise norms call 18 to 24% acceptable for men and 25 to 31% for women, with fitness at 14 to 17% and 21 to 24%. Obesity starts at 25% for men and 32% for women. Essential fat, the minimum for normal function, is 2 to 5% for men and 10 to 13% for women.
Hodgdon and Beckett fitted separate equations for Navy men and Navy women, because the two groups store fat in different places. The published female equation uses waist plus hips minus neck, while the male equation uses waist minus neck alone. A man's hip measurement is therefore not used anywhere, and the page hides that box for men.
A reading below 2% or above 60% means the measurements are outside anything the equations were fitted on, usually because of a very thick neck, a very small waist, or a typing slip. Re-measure carefully. If the numbers are right, this method is simply the wrong tool for that body shape.
Formula only: no rates or limits are read from an official source.
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Also works as: Navy Body Fat Calculator.
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