How the US Navy Method Works
Developed at the Naval Health Research Center, the circumference method estimates body density from where your body actually stores fat: the waist-to-neck difference for men, and waist + hip − neck for women, each scaled logarithmically against height. Validated against underwater weighing, it lands within roughly ±3–4% for most people — remarkably good for a tape measure, and far more informative than scale weight alone.
Use it to track trends: measure the same way at the same time of day, weekly, and watch the direction, not single readings. Pair it with the BMI Calculator for the classic screening number, the BMR Calculator to know your resting burn, and the Calorie Calculator to plan a cut or lean bulk around your lean mass.
Frequently Asked Questions
How does the US Navy body fat method work?
It estimates body density from tape measurements — men: waist − neck vs height; women: waist + hip − neck vs height — in a log formula validated against underwater weighing. Accuracy is about ±3–4% for most people.
What is a healthy body fat percentage?
ACE ranges — men: essential 2–5%, athletes 6–13%, fitness 14–17%, average 18–24%, obesity 25%+. Women: essential 10–13%, athletes 14–20%, fitness 21–24%, average 25–31%, obesity 32%+.
How do I take the measurements correctly?
Neck just below the larynx; waist at the navel (men) or narrowest point (women) after a normal exhale; hips at the widest point (women). Bare skin, level tape, never pulled tight — measure twice and average.
Is body fat percentage better than BMI?
They complement each other: BMI is a quick weight-for-height screen that can misread muscular people; body fat % separates fat from lean mass. Tracking both plus waist size gives the best simple picture.
Are my measurements uploaded anywhere?
No — everything is calculated in your browser. Your measurements are never sent, stored or logged.