How the Navy Method Works
The US Navy body fat formula estimates body fat percentage from simple circumference measurements — neck, waist, and (for women) hips — along with height. It was developed by Hodgdon and Beckett at the Naval Health Research Center and remains the standard method used by the US military for body composition assessment.
Women: BF% = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
All measurements in centimeters.
What Is FFMI?
Fat-Free Mass Index (FFMI) normalizes your lean mass relative to your height — think of it as BMI but for muscle instead of total weight. It's calculated as lean mass in kg divided by height in meters squared, with a small height correction. An FFMI of 25 is roughly the natural ceiling for most men; values above 25-26 are extremely rare without pharmaceutical assistance.
Body Fat Categories
Body fat ranges vary by sex. The categories below are general guidelines — individual health depends on many factors beyond body fat percentage alone.
How Accurate Is This?
The Navy method has a typical error margin of ±3-4%. It's less accurate than DEXA or hydrostatic weighing, but far more practical. For tracking changes over time, consistency matters more than absolute accuracy — measure in the same conditions each time.