Body Fat Percentage Calculator (US Navy Method)

Calculator

How we calculate it

This calculator implements the Hodgdon–Beckett circumference equations developed at the Naval Health Research Center and specified in the US Department of Defense body composition program. For men the equation uses the abdominal circumference measured at the navel, the neck circumference measured below the larynx, and height. For women it uses the natural waist, the hip at its widest point, the neck, and height. Both equations are logarithmic and were published with measurements in inches, so entries in centimeters are converted to inches before the equation is applied rather than an approximate metric restatement being used. Published accuracy against criterion methods such as underwater weighing is in the region of three to four percentage points, which means a result of 22% is consistent with a true value somewhere around 18 to 26%. That is why the calculator is most useful for tracking a trend in your own measurements, taken the same way each time, rather than for a single precise figure. No category band is shown alongside the percentage. There is no equivalent of the WHO BMI classification for body fat, and the essential–athletic–fitness–average tables widely reproduced online come from individual organizations and fitness conventions rather than from a clinical guideline; presenting one as a standard would imply an authority it does not have.

Important limitations

• This is an estimate from tape measurements, not a measurement of body composition. Published accuracy is roughly three to four percentage points either way against criterion methods.
• The equations were fitted on US Navy personnel, a population younger and narrower in body composition than the general public, and accuracy falls outside that range — particularly in older adults, in very lean people and at higher body weights.
• Tape placement dominates the result. A one-inch error in the abdominal measurement can move the estimate by several percentage points, and measuring after a meal or at a different time of day will change it.
• No health band is shown for the percentage, because no guideline body publishes one comparable to the WHO BMI classification. The tables circulated online are organizational conventions rather than clinical guidance.
• Only two published equations exist, for men and for women, and they are structurally different — the one for women requires a hip measurement. There is no published third form.
• The equations are not validated during pregnancy, in children and adolescents, in people with significant edema or ascites, or after limb amputation.
• Body fat percentage describes composition, not health, and it is not a diagnosis of anything.