How the Navy Body Fat Method Works
The U.S. Navy tape method estimates body density from circumference ratios, waist vs neck for men, waist + hips vs neck for women, adjusted by height, then converts density to body fat %. Unlike BMI, which confuses muscle with fat, it separates fat mass from lean mass with accuracy around ±3 to 4% of DEXA scans when measured carefully. From there, protein targets scale with weight and activity (1.2 to 2.2 g/kg) and water needs scale with weight plus exercise.
Men: 495 / (1.0324 − 0.19077·log10(waist−neck) + 0.15456·log10(height)) − 450
Women add hip: log10(waist + hip − neck) · Protein 1.2 to 2.2 g/kg · Water 35 ml/kg + 0.5 L/hr exercise
Worked Example
Scenario: male, 178 cm, 80 kg, 40 cm neck, 85 cm waist, 3 hrs/week exercise
Body Fat
~14.9%
Lean Mass
~68 kg
Protein Target
128 to 176 g/day
Water Target
~3.0 L/day
Measure at the navel (men) or narrowest waist + widest hips (women), tape level and snug, not compressing skin. Morning, unfed measurements track best.
What the Calculator Shows
- Body fat %, Navy-method estimate from your tape measurements
- Fat mass & lean mass, kilograms of each for goal-setting
- Protein range, daily grams scaled to weight and training load
- Water target, daily liters including exercise top-up
Use It With Your Nutrition Plan
Pair your protein target with calories from our TDEE Calculator and macro splits from our Macro Calculator. Recheck monthly, waist trends beat scale weight for tracking recomposition. For general feedback this is educational only, not medical advice.