How to Calculate Body Fat Percentage
This calculator uses the U.S. Navy circumference method, a validated formula that estimates body fat from simple tape measurements. Developed at the Naval Health Research Center in 1984, it was the tape-test method behind U.S. military body composition checks for four decades. Since 2026 the services screen with a waist-to-height ratio instead (the Navy keeps a sex-specific height-minus-waist table as a second step), so this formula is no longer what a fitness assessment records. It remains the best free estimate of body fat percentage for general use.
The Navy Method Formula
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
All measurements in centimeters.
How to Take Measurements
- Waist: At the navel, standing relaxed (don't suck in)
- Neck: Below the Adam's apple at the narrowest point
- Hip (women only): At the widest point of buttocks, feet together
- Height: Without shoes, standing straight
Body Fat Categories
- Essential fat: Men 2-5%, Women 10-13% — minimum for survival
- Athletes: Men 6-13%, Women 14-20%
- Fitness: Men 14-17%, Women 21-24%
- Acceptable: Men 18-24%, Women 25-31%
- Obese: Men 25%+, Women 32%+
Why Body Fat Matters More Than Weight
Two people can weigh the same but have very different body compositions. Someone with 15% body fat carries more muscle (and less health risk) than someone at 30% body fat, even at the same weight. Body fat percentage gives a more accurate picture of health than BMI or scale weight alone.
Measurement Methods Compared
- Navy method (this calculator): Free, requires only a tape measure. Accurate within 1-3% for most people
- Skinfold calipers: $10-30, measures skin folds at 3-7 sites. Accuracy depends on technique (±3-4%)
- Bioelectrical impedance (BIA): Found in smart scales. Convenient but affected by hydration, meals, and exercise (±3-5%)
- DEXA scan: $50-150 per scan. Gold standard accuracy (±1-2%). Uses low-dose X-ray
- Hydrostatic weighing: $40-100. Very accurate but requires full submersion in water
How to Reduce Body Fat
- Calorie deficit: Eat 500 calories below your TDEE for ~1 lb fat loss per week
- Resistance training: Preserves muscle during a deficit, so more of the weight lost is fat
- Protein intake: 0.7-1g per lb bodyweight helps maintain muscle while losing fat
- Consistency over intensity: Moderate, sustainable deficits outperform crash diets long-term
Consider using this alongside our BMI Calculator and TDEE Calculator for a complete fitness assessment.
Body Fat and Athletic Performance
Body fat percentage significantly impacts athletic performance. Endurance athletes like marathon runners typically maintain 6-13% (men) or 14-20% (women) body fat for optimal power-to-weight ratio. Strength athletes like powerlifters often compete at higher body fat levels (15-25%) because the additional mass aids force production. Bodybuilders temporarily drop to 3-6% (men) or 10-14% (women) for competition, but these levels are not sustainable long-term and can impair hormone function, immune response, and recovery.
Essential Fat vs. Storage Fat
Not all body fat is the same. Essential fat — found in bone marrow, organs, the central nervous system, and cell membranes — is required for normal physiological function. Men need a minimum of about 2-5% essential fat; women need 10-13% due to additional fat in breast tissue, uterus, and other sex-specific areas. Storage fat is the subcutaneous and visceral fat that serves as an energy reserve. Subcutaneous fat (under the skin) is relatively benign; visceral fat (around internal organs) is metabolically active and strongly associated with type 2 diabetes, cardiovascular disease, and inflammation. Waist circumference is a better predictor of visceral fat than total body fat percentage.