Body Fat Calculator - US Navy Method

How the US Navy Body Fat Method Works

The US Navy circumference method, developed by Hodgdon and Beckett at the Naval Health Research Center in 1984, estimates body fat from just a tape measure. For men it uses height, neck, and waist; for women it adds the hip measurement because women store proportionally more fat around the hips. The formula converts these circumferences through logarithms into a body density estimate and then into a fat percentage. Against underwater weighing it is accurate to within about 3-4 percentage points for most people.

Measurement technique matters more than the math. Use a flexible, non-stretch tape held snug but not compressing the skin. Men measure the waist horizontally at the navel; women at the narrowest point of the torso and hips at the widest point. Measure the neck just below the larynx, sloping slightly downward to the front. Take each measurement two or three times in the morning before eating and use the average, since a single sloppy measurement can swing the result by two points or more.

The category table comes from the American Council on Exercise. For men, 2-5% is essential fat, 6-13% typical for athletes, 14-17% fit, 18-24% average, and 25%+ classified as obese. For women the bands sit roughly 8-10 points higher because essential fat requirements are greater: 10-13% essential, 14-20% athletes, 21-24% fitness, 25-31% average, 32%+ obese. Body fat percentage is generally a better health signal than BMI alone, since BMI cannot separate a muscular 90 kg from a sedentary 90 kg.

If you also enter your weight, the calculator splits it into fat mass and lean mass (muscle, bone, organs, water). Tracking lean mass during a diet tells you whether you are losing fat or muscle: losing 3 kg while lean mass holds steady is a win, losing 3 kg of which 2 kg is lean mass is a warning to raise protein and keep lifting. Pair this tool with the Macro Calculator to set protein targets and the BMI Calculator for a complementary baseline.