Body Fat Calculator (Circumference Method)

This body fat calculator gives a method-specific circumference estimate of body-fat percentage from neck, waist, and hip measurements, then applies that percentage to body weight to show estimated fat mass and lean mass. It does not assign a health, fitness, or military-compliance category.

Measurements and units

Choose imperial or metric and the male or female equation. The starting male example uses 70 in height, 180 lb weight, a 15 in neck, and a 34 in waist. The female equation also requires hip circumference; its starting hip value is 37 in.

Metric measurements are converted to inches before the same equations are used. Supply consistently measured circumference values and retain the same measurement approach for comparisons. This page does not establish anatomical measurement sites.

All entered measurements and weight must be positive. For the male equation, waist must exceed neck. For the female equation, waist plus hip must exceed neck.

Legacy calculator coefficient set v1

The following coefficients are retained as a transparent legacy calculator assumption. This page does not attribute them to a service or measurement protocol.

With measurements in inches, the male estimate is:

$\frac{495}{1.0324-0.19077\log_{10}(W-N)+0.15456\log_{10}(H)}-450$

The female estimate is:

$\frac{495}{1.29579-0.35004\log_{10}(W+Hip-N)+0.221\log_{10}(H)}-450$

Here, $W$ is waist, $N$ is neck, and $H$ is height. Estimated fat mass is body weight multiplied by the percentage divided by 100; estimated lean mass is weight minus fat mass.

For the starting male measurements, the circumference estimate is 11.1%. At 180 lb, that gives 19.9 lb estimated fat mass and 160.1 lb estimated lean mass. The result is internally consistent because $19.9+160.1=180.0$ lb, apart from display rounding.

Measurement-repeat workflow

Use the result to compare like with like:

1. Repeat each circumference using the same measurement approach.
2. Record the unit system, equation selection, measurements, and date.
3. Compare the unrounded measurements before attributing a changed percentage to body composition.
4. For a weight-and-height screening calculation instead, use BMI. For an official Army task, go to the separate Army body-fat calculator.

Limits

This is an equation estimate, not a direct measurement of tissue. Input and measurement differences can change the result. Derived fat and lean masses inherit the same uncertainty. Do not use this educational legacy calculation as an official determination or clinical decision.

Sources

• CDC, Adult BMI Categories — distinction between population screening and individual diagnosis.

• PMC11026907 — Peer-reviewed article (Obesity Science & Practice, 2024) documenting the sex-specific Hodgdon circumference equations the U.S. military adopted in 2002 — the same legacy coefficient set the worksheet reproduces — and their population-level estimation limits.

• VALIDITY OF THE NAVY CIRCUMFERENCE BODY FAT.918 — Peer-reviewed validity study (Medicine & Science in Sports & Exercise, 2003) comparing Navy circumference body-fat estimates with hydrostatic weighing in men; supports the page’s statement that the result is an equation estimate, not a direct measurement of tissue.