Body Fat Percentage Calculator

Estimate body fat percentage using Navy method from waist, neck, hip, and height measurements.

  • Math & Calculators
  • Runs in your browser
  • Free, no signup

The guide

Tested tool guide Tested browser tools Checked August 16, 2026

What Body Fat Percentage Calculator does, with a checked example

This calculator estimates body fat percentage from tape measurements and height, using the U.S. Navy circumference method, the same equations the armed services use for their tape test. Men enter height, neck, and waist measured at the navel; women enter height, neck, waist at its narrowest point, and hips at their widest. The result is a prediction, not a measurement: circumference equations estimate body density and carry an error band of several percentage points against DEXA or hydrostatic weighing. What surprises most people is how much tape placement matters - an inch of error moves the answer one to two points.

Worked example

A concrete input and expected output from the current implementation.

Input

Female, 65 in tall, neck 12 in, waist 28 in, hip 38 in

Expected output

Estimated body fat: 27.3%

The women's Navy equation is 163.205 * log10(waist + hip - neck) - 97.684 * log10(height) - 78.387, all in inches. Here waist + hip - neck = 54, log10(54) = 1.7324, and log10(65) = 1.8129, so the result is 163.205 * 1.7324 - 97.684 * 1.8129 - 78.387 = 282.735 - 177.093 - 78.387 = 27.26, which rounds to 27.3%.

How the result is produced

1

What it computes

The tool applies the published Navy equations, which take base-10 logarithms of circumference combinations and height. For men: 86.010 x log10(waist - neck) - 70.041 x log10(height) + 36.76. For women: 163.205 x log10(waist + hip - neck) - 97.684 x log10(height) - 78.387. The constants assume inches throughout, so any centimeter input must be converted to inches before the logarithms are taken.

2

Measurement sites

The equations only behave if the tape lands on the official sites. Men measure the abdomen horizontally at the navel, not the trouser-line waist. Women measure the waist at its narrowest point and the hips at their widest. The neck is measured just below the larynx. Because the formulas take logarithms of small differences, an inch of misplaced tape changes the result by roughly one to two percentage points.

Good uses

  • Monthly tracking during a cut or bulk: tape measurements cost nothing and, taken at the same sites each time, show whether body fat is trending down while the scale weight stalls.
  • Pre-screening against the armed forces body-fat standard before an Army or Navy tape test, which uses these same equations.
  • Getting a body-fat baseline for a diet or training plan when a DEXA scan or gym impedance scale is unavailable or untrusted.

Limits and checks

  • It is an estimate with a wide error band: circumference methods agree with DEXA and hydrostatic weighing only to within several percentage points, so a single reading is not a diagnosis. Changes over time, measured the same way at the same sites, are more reliable than the absolute number.
  • Site and unit mistakes dominate the error. Men must measure at the navel, not the belt line, and women at the narrowest waist and widest hip; the neck is read just below the larynx. Entering centimeters where inches are expected, or mixing units, breaks the equation.
  • Not every 'Navy method' calculator implements the same equation. Some use the density-based original form converted to fat percentage with Siri or Brozek equations, while others use the direct percentage form shown here, and the two can differ by several points. Hydration and tape tension add further noise.

Common questions

Why is my result a few points different from my smart scale?

The two methods estimate different things. This tool predicts body density from circumference ratios, while impedance scales infer fat from electrical resistance, which shifts with hydration. Both carry an error band of several percentage points, so a gap of three or four points is normal. Watch the direction of change over weeks, not the single number.

Is this the official military test, and can I use it to check a service standard?

The Army, Navy, and Marine Corps use the same equations for their official tape tests, so the math matches. But official screens follow strict measurement procedures, and each service sets its own age- and sex-based maximum percentages, which are revised over time. For a job, waiver, or recruitment decision, check the current regulation for your service rather than relying on the number alone.

References and verification

The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.