Body Fat Percentage Calculator

This calculator estimates body fat percentage using the US Navy method, which is based on circumference measurements. For men, you need neck and waist measurements; for women, neck, waist and hip measurements. The formula uses the logarithmic relationship between these measurements and height to estimate body fat.

Healthy body fat ranges vary by sex and age. For men, 10–20% is generally considered healthy; for women, 18–28%. Essential fat levels (below which health is compromised) are around 3–5% for men and 10–13% for women. Athletes typically sit at the lower end of the healthy range.

Measure at the narrowest point of the neck, the navel for waist (men) or the narrowest point (women), and the widest point for hips. Take measurements on bare skin, standing relaxed. For best accuracy, measure in the morning before eating. The Navy method has an accuracy of roughly ±3–4% compared to DEXA scans.

Body fat percentage — what's healthy? NHS/American Council on Exercise ranges: Essential fat 10-12% (women), 2-4% (men). Athletes 14-20% (W), 6-13% (M). Fitness 21-24% (W), 14-17% (M). Average 25-31% (W), 18-24% (M). Obese 32%+ (W), 25%+ (M). Women naturally carry more body fat due to oestrogen and reproductive biology. BMI alone is misleading — a muscular 100kg rugby player at 1.85m has BMI 29.2 (overweight) but might be 12% body fat (elite athlete).

Methods to measure body fat — accuracy ranking. DEXA scan: gold standard, ±1-2% accuracy, £80-£150 private clinics. Hydrostatic weighing: ±2%, available at sports science labs. BodPod (air displacement): ±2-3%, NHS hospitals and some gyms. Skinfold calipers (3-7 site): ±3-5% with skilled practitioner. Bioelectrical impedance (gym scales, smart scales): ±5-10%, varies with hydration. Tape measure methods (US Navy, YMCA): ±5-8%. Visual estimation: ±10%. Most reliable home option: skinfold calipers + spreadsheet, training takes practice.

UK Navy / Hodgdon equation — what this calculator uses. Men: %BF = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76. Women: %BF = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387. Measurements in inches/cm depending on version. Used by US/UK military for fitness screening because tape measures are cheap and reliable. Accuracy ±3-4% vs DEXA for general population.

Visceral vs subcutaneous fat — why location matters. Subcutaneous fat (under skin, especially hips/thighs/buttocks): cosmetic concern but limited health impact. Visceral fat (around organs — liver, intestines, pancreas): strongly linked to type 2 diabetes, heart disease, fatty liver, stroke. Waist circumference is the best home proxy: NHS targets — under 94cm men (102cm = high risk), under 80cm women (88cm = high risk). Waist-to-height ratio under 0.5 ideal — 'keep your waist less than half your height'.

How to reduce body fat safely. Sustainable rate: 0.5-1% body fat per month. Caloric deficit: 500 kcal/day deficit = ~0.5kg/week loss; 1,000 kcal/day = ~1kg/week (NHS upper limit). Protein intake critical to preserve muscle: 1.6-2.2 g/kg bodyweight daily during deficit. Strength training prevents 'skinny fat' outcome — without resistance, 25-50% of weight loss can be muscle. Cardio for energy expenditure but doesn't shift body composition without strength work. Sleep 7-9 hours: under 6 hours sabotages fat loss (cortisol drives visceral fat storage).