HealthCalc

Body composition

Body fat calculator

A tape measure, four numbers, and an equation from 1984. The US Navy circumference method was built to estimate body fat without a clinic, and it is the most widely used one that does not need a machine.

Method: Hodgdon & Beckett 1984 (US Navy) · the 1984 technical report
Unit system
The 1984 method uses a different equation for each. There is no single unisex form.

Measure at the narrowest point. The neck is below the Adam's apple and above the collarbone; the abdomen is at the navel, relaxed, not pulled in. The hip field appears for the female equation, which uses it, and hides for the male equation, which does not.

No age field, on purpose. The 1984 paper tested age and body weight against the estimate and they did not improve it, so they were left out of the equations. Asking for your age here would suggest it changes the answer when it does not.

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How to use this calculator

  1. Pick your unit system. Every measurement switches with it.
  2. Enter height, then neck and abdomen. Women also enter hips.
  3. Read the percentage and the error of the method beside it.
  4. Copy the link if you want to keep or share this exact result.

The error shown with the result — roughly 3–4 percentage points — is the authors' own figure for how far a true value is likely to sit from the estimate. It is larger than the precision of the answer, which is why the result is rounded to one decimal place and no further.

The formula

BD = 495 ÷ body density − 450, all in centimetres
Men: density = 1.0324 − 0.19077 + 0.15456 × 10−10(abdomen − neck)
Women: density = 1.29579 − 0.35004 + 0.22100 × 10−10(abdomen + hip − neck)

Body density then becomes body fat through the Siri equation, which the same authors used to convert their measured values. The centimetre form is used directly; the centimetre and inch forms of the original paper differ slightly in their coefficients.

Why there is no "healthy" band here

Most body fat pages end with a coloured bar telling you whether you are underfat, athletic, fit, average or obese. Those bands are commercial convention. They are not published by the American College of Sports Medicine, the CDC, or the authors of the method, and they disagree with each other by several percentage points depending on who is selling the chart.

This page therefore gives you the number and its error, and leaves the judgement to you and a professional who knows your training history. If you need a category, a DEXA scan or a clinical assessment will tell you far more than a circumference estimate can.

Source

Hodgdon, J. A. & Beckett, M. B. (1984). Prediction of percent body fat for U.S. Navy men from body circumferences and height. Naval Health Research Center, San Diego, Report No. 84-11. The companion report for women, using a different equation, is No. 84-29. Both were summarised in Medicine & Science in Sports & Exercise 16(2), 1985.

Population covered: the sample was U.S. Navy personnel — active duty and reserve, mostly men, with a smaller female group. The method is now the basis of the US Navy circumference method and is widely used outside the military, but the validation population is not the general public. Do not assume the stated error applies to elite athletes, to people at either extreme of body fat, or to children.

Frequently asked questions

Is this as accurate as a DEXA scan?

No. DEXA is far more accurate, and so is a clinical estimate, but it costs money and needs equipment.

Why no age field?

The original study tested age and body weight as candidate variables and neither improved the estimate, so neither is in the equation.

What if my measurements are slightly off?

A centimetre of error on the abdomen moves the result by well under a percentage point, which is much smaller than the method's own 3–4 point error.