Overview
This tool estimates body fat from neck, waist and hip circumferences using published US Navy equations. The result is useful for tracking a general trend, but it is not a laboratory measurement.
Formula
The equation uses circumference differences and height. For men, neck is subtracted from waist; for women, hip is added to waist and neck is subtracted. The result is an estimated percentage of body weight.
How it works
Measure carefully
Use a non-stretch tape on skin or light clothing, take three readings and average them.
Enter sex and measurements
Hip is required for women only; waist is measured at the level specified for each sex.
Read the percentage and mass
The result shows body fat percentage, fat mass and lean mass.
Worked examples
Man, 80 kg
180 cm height, 38 cm neck and 90 cm waist give an estimate of about 20%.
Woman, 60 kg
165 cm height, 33 cm neck, 75 cm waist and 100 cm hip give about 30%.
Frequently asked questions
Is the result accurate?
It can differ from DEXA or bioimpedance by several percentage points. Use it to track a trend with the same measuring method, not as an absolute number.
What is a normal body fat percentage?
It varies by sex and age. A common average range is about 14–24% for men and 21–31% for women, but health context matters more than one number.
Why is hip circumference needed?
The female equation uses hip because fat distribution differs between sexes.
Is it suitable for athletes?
It may under- or overestimate in very muscular people. Use specialized assessment when precision matters.
This calculator is for educational and informational purposes only and is not a substitute for professional advice.