Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Estimate body fat percentage using the US Navy circumference method.
17.4%
This tool estimates body fat percentage using the US Navy circumference method (Hodgdon & Beckett, 1984) -- a tape-measurement-based formula the US military actually uses for body-fat screening, requiring only a few circumference measurements rather than calipers or a scan.
Enter your sex, height, neck, and waist circumference (women also enter hip circumference). Your estimated body fat percentage appears instantly.
Men: 495 / (1.0324 - 0.19077 × log10(waist - neck) + 0.15456 × log10(height)) - 450
Women: 495 / (1.29579 - 0.35004 × log10(waist + hip - neck) + 0.221 × log10(height)) - 450
Measure at the same time of day (morning, before eating) for consistency, and measure snugly but without compressing skin. This is an estimate -- for the US Army's own distinct formula, see the Army Body Fat Calculator. Not a substitute for a DEXA scan or clinical assessment.
Take a hypothetical man who is 70 inches tall with a 15-inch neck and a 34-inch waist. These are the values the calculator starts with. The waist minus neck difference is 19 inches. Putting the numbers into the men's equation (logarithms to base 10) gives a body fat estimate of about 17.4 percent. If the same man measured his waist at 38 inches instead, the difference becomes 23 inches and the estimate rises to about 24.5 percent, which shows how sensitive the method is to the waist measurement. A one-inch error at the waist changes the answer by more than a one-inch error anywhere else, so that is the measurement worth taking most carefully.
Height, neck, waist and, for women, hip are all entered in inches, and the result is a percentage. If you measured in centimetres, divide by 2.54 first. The tool needs each measurement to be positive, and the waist must be larger than the neck, because the formula takes the logarithm of the waist minus neck difference for men. For women the hip field appears only when the female option is selected, and it is needed for the calculation. If any requirement is unmet, the result area stays empty and explains what to enter.
The tool uses the US Navy circumference method (Hodgdon and Beckett), written as a body-density equation in centimetres. Because your measurements are entered in inches, the tool converts them to centimetres before applying the equation. The Army Body Fat Calculator on this site uses the same underlying method in its inch and base-10 logarithm form, so the two give nearly the same answer for the same tape measurements.
This is a screening estimate, not a body scan. Circumference formulas assume typical body shapes, so people with unusually thick necks, very muscular builds, or fat distributed differently from the reference groups may see results that are off by several points. Small changes in measurements can also produce visible jumps in the result. The tool floors the answer at zero percent, so an implausibly low reading means your inputs likely do not fit the formula, not that you have no body fat. Use the same method, same time of day and same tape each time when you track changes, and pay more attention to the trend across measurements than to the exact value on any one day.
Body fat estimates are not a diagnosis. If you are worried about your health, weight or eating, speak with a doctor or registered dietitian. This page is educational only.
It's a widely used field estimate with reasonable accuracy for most body types, but circumference-based methods are less precise than DEXA scans or hydrostatic weighing.
It accounts for typical differences in fat distribution patterns between sexes, using an additional hip measurement for women.
Commonly cited "fitness" ranges are roughly 14-24% for men and 21-31% for women, though healthy ranges vary by age and individual factors -- consult a healthcare provider for personalized guidance.
The equation takes the logarithm of waist minus neck (for women, waist plus hip minus neck), which is only defined for positive values.
The fields are labeled in inches. Divide centimetre measurements by 2.54 before entering them.
The hip measurement is only shown, and only used, when the female option is selected.
The estimate depends heavily on the waist minus neck difference, so an error of an inch at the waist has a large effect. Measure carefully and average several readings.
Reference: Centers for Disease Control and Prevention