Body Fat Calculator · Practical guide
The Navy Method Body Fat Formula
The exact equations behind the tape-test body fat estimate, with a worked example you can check yourself.
At a glance
The Formulas
The U.S. Navy method, developed by Hodgdon and Beckett in 1984, estimates body fat from circumferences and height using base-10 logarithms. For men (measurements in inches):
BFP = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
For women, the hip circumference joins the waist before the neck is subtracted:
BFP = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
Use one unit system throughout — all inches or all centimeters. The calculator above applies these equations for you and then uses your weight to split the result into fat mass and lean mass.
Interactive tool
Body Fat Calculator
Enter your own values, then compare the result with the examples below.
A Worked Example
A man who is 70 inches tall with a 36-inch waist and a 15-inch neck: waist minus neck is 21, log10(21) ≈ 1.3222, and log10(70) ≈ 1.8451. So BFP = 86.010 × 1.3222 − 70.041 × 1.8451 + 36.76 ≈ 21.3%, which lands in the Average category for men. At 190 pounds, that is roughly 40.4 pounds of fat mass and 149.6 pounds of lean mass.
Why the Formula Uses Logarithms
Body density does not scale linearly with circumference, so the equations use log10 to model how girth relates to height. That is also why small measuring errors matter: a half-inch error at the waist can swing the result by a full percentage point or more.
How Accurate Is It?
The Navy method typically lands within 3 to 4 percentage points of DEXA or hydrostatic weighing — not lab-grade, but excellent for tracking trends at home for free. It is the same tape test the U.S. military uses for service members who exceed weight-for-height limits.
Frequently Asked Questions
Do I need a special tape measure for the Navy formula?
No. Any flexible, non-stretch tape works, including a sewing tape. A self-tensioning body tape makes solo measurements easier and more repeatable.
Can I use centimeters instead of inches?
Yes, as long as every measurement — waist, neck, hip, and height — uses the same unit. The equivalent centimeter form of the equation produces the same result within rounding.
Why does the Navy formula ignore body weight?
The percentage comes from circumferences and height alone. Weight is only used afterward to convert the percentage into fat mass and lean mass numbers you can track in pounds or kilograms.
What if my result comes out negative or above 100%?
That means the measurements are inconsistent with the formula's assumptions — usually a waist measured smaller than the neck or a unit mix-up. Re-measure carefully and confirm every value uses the same units.