What is the Body Fat Calculator?
Body-fat percentage tells you far more about your health and physique than weight or BMI alone, because it separates fat mass from muscle, bone, and water. Two people with identical BMI can look and perform completely differently depending on their body composition.
The U.S. Navy circumference method estimates body fat from simple tape measurements — height, neck, and waist (plus hips for women). Developed for military fitness assessments, it correlates well with laboratory methods (typically within 3-4%) and requires no special equipment.
Body Fat Calculator Formula & How It Works
- All measurements in centimetres
- Women add hip circumference: log₁₀(waist + hip − neck)
- Waist: at the navel (men) / narrowest point (women)
- Neck: just below the larynx
The formula uses the strong statistical relationship between girth measurements and total body density. Measure in the morning before eating, with the tape snug but not compressing the skin, and take each measurement twice for accuracy.
Worked Examples
Man: 175 cm tall, 85 cm waist, 38 cm neck
Body fat ≈ 18.3% — within the 'Average' range (18-24%) for men. At 75 kg that's roughly 13.7 kg fat mass and 61.3 kg lean mass.
Woman: 162 cm tall, 70 cm waist, 95 cm hip, 32 cm neck
Body fat ≈ 26.3% — within the healthy 'Average' band (25-31%) for women.
Expert Tips
- Measure at the same time of day each week — consistency matters more than absolute accuracy for tracking change.
- Pair the tape test with progress photos; circumference methods can lag rapid recomposition.
- Healthy ranges: men 8-19%, women 21-32% — essential fat minimums are ~3% (men) and ~12% (women).