Body Fat Calculator

How the Navy Method Works

The US Navy method uses circumference measurements to estimate body fat. For men, the formula uses height, waist circumference, and neck circumference. For women, it also includes hip circumference. These measurements are plugged into a logarithmic equation developed by Hodgdon and Beckett (1984) that has been shown to correlate closely with hydrostatic weighing results.

Measurements, units and a worked example

Measure the neck below the Adam's apple. For the male equation, measure the abdomen at the navel; for the female equation, use the natural waist and the widest part of the hips. Measure the waist after a relaxed exhalation. Select the matching unit for each input.

The equations use inches internally (1 inch = 2.54 cm). For example, the male equation with height 175 cm, waist 85 cm and neck 38 cm gives approximately 17.0%. At 80 kg, that corresponds to about 13.6 kg of fat mass and 66.4 kg of lean mass. Lean mass includes more than muscle.

Formula and measurement reference: US Coast Guard body-composition manual, pages 2-7–2-9. We retain input precision instead of applying military assessment rounding; this tool is not an official service assessment.

Limitations

The Navy method may be less accurate for individuals with unusual body proportions, very high or very low body fat levels, or significant muscle mass. It relies on tape measurements, which introduce operator error. For the most accurate results, measure in the morning before eating, keep the tape snug but not compressing the skin, and take each measurement twice. A qualified healthcare professional can help interpret body-composition measurements.