How to use
This calculator estimates the proportion of body mass represented by fat from height and body circumferences. It uses the historical male or female circumference equation often called the Navy tape method. The result is an estimate for an adult, not a reading from a body-composition instrument. Select the equation whose original reference group is relevant; the two equations use different measurement sites, not interchangeable labels.
Select the equation and measurement unit. Enter height without shoes and the requested circumferences. The same unit applies to every measurement. The male equation uses height, neck and abdomen; the female equation also needs hips and uses the natural waist instead of the navel.
Press Calculate or Enter to confirm the result. Editing a number or choice clears the confirmed result and disables Copy. Calculate again after editing. Copy result includes the estimate and its limitation. Clear removes your entries and result while preserving choices; gray examples may return in empty fields.
Tape measurement locations
Use a flexible, non-stretch tape. Keep it in contact with the body without squeezing the skin. Stand normally, look forward and keep the shoulders relaxed. Ask someone to help if the tape cannot be kept level. Take repeat readings when placement is uncertain.
H: measure standing height without shoes. N: measure the neck just below the larynx, perpendicular to the neck’s long axis. W in the male equation: measure the abdomen horizontally through the navel after a normal relaxed exhalation. W in the female equation: measure the smallest natural waist, usually between the navel and the lower end of the breastbone, after a relaxed exhalation. P: measure hips around the greatest projection of the buttocks, horizontally; only the female equation uses this value.
The diagram is a schematic of tape locations, not a model of your body shape. It switches the waist location for the selected equation and displays your current measurements. A pants size is not a circumference measurement. Keep height and circumferences in the selected unit; do not mix centimeters, feet and inches.
Method and meaning
All lengths are converted to inches first (1 in = 2.54 cm). For the male equation: 86.010 × log10(W − N) − 70.041 × log10(H) + 36.76. For the female equation: 163.205 × log10(W + P − N) − 97.684 × log10(H) − 78.387. Log10 is the base-10 logarithm. Intermediate values are not rounded; only the displayed answer is rounded to at most two decimal places.
Worked examples
Male example: H = 180 cm, N = 38 cm and W = 90 cm gives approximately 19.93%. The hip field does not affect this equation.
Female example: H = 165 cm, N = 34 cm, W = 75 cm and P = 100 cm gives approximately 29.24%. Enter all four measurements; leaving out the hip changes the calculation completely.
Scope and input checks
This implementation uses continuous measurements rather than military half-inch rounding or pass/fail tables. It does not certify current Navy, Army or Coast Guard eligibility. The formula source is historical; the software does not claim a universal validated accuracy, an individual confidence interval or suitability for every body type.
Only generally healthy adults aged 19+ are supported here. Children, pregnancy, breastfeeding, medical conditions and prescribed nutrition or fluid restrictions are outside the tool’s scope. Positive measurements up to 304.8 cm / 120 in are accepted as a software guard, not a clinically validated range. A nonpositive logarithm input or a result outside 0–100% is rejected. A plausible-looking number still does not establish accuracy.
Questions
Why can another calculator differ?
Different equations, tape sites, centimeter/inch handling and intermediate rounding can change the estimate. Compare the same method and measurements before comparing the numbers.
Is this the same as a body-fat scale or DXA?
No. Those methods use different measurements and assumptions. A tape calculator does not obtain electrical impedance or scan data.
Does this tell me whether my body is healthy?
No. There are no appearance labels, ideal-body targets, risk categories or weight-loss prescriptions here. Discuss a clinical question with a qualified professional.
Why does the hip value do nothing in the male equation?
That equation contains only neck, abdomen and height. The hip field and the diagram’s P value are relevant only to the female equation.