Body Fat Calculator

BMI doesn't distinguish between fat and muscle — body fat percentage does. This calculator estimates your body fat percentage using the US Navy Method (circumference measurements) or BMI-based estimation, giving you a clearer picture of your body composition.

How to Use This Calculator

1. Select your gender.
2. Enter your height and weight.
3. For US Navy Method: measure and enter waist circumference (at navel level), neck circumference (below larynx), and for women: hip circumference (widest point).
4. Click Calculate to see body fat percentage, fat mass, and lean mass.

US Navy Method Formula

Men: %BF = 86.01 × log₁₀(abdomen − neck) − 70.041 × log₁₀(height) + 36.76

Women: %BF = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387

All measurements in inches. Results are estimated — for clinical precision, use DEXA scan or hydrostatic weighing.

Body Fat Percentage Categories

• Essential fat (minimum): 2–5% (men), 10–13% (women)
• Athletes: 6–13% (men), 14–20% (women)
• Fitness: 14–17% (men), 21–24% (women)
• Average/Acceptable: 18–24% (men), 25–31% (women)
• Obese: 25%+ (men), 32%+ (women)

Example Calculation

Male | Height: 70 inches | Neck: 15 in | Waist: 36 in

• %BF = 86.01 × log₁₀(36−15) − 70.041 × log₁₀(70) + 36.76
• = 86.01 × 1.322 − 70.041 × 1.845 + 36.76
• = 113.72 − 129.23 + 36.76 ≈ 21.3%
• If weight = 185 lbs: Fat mass ≈ 39.4 lbs | Lean mass ≈ 145.6 lbs

Common Mistakes to Avoid

• Measuring waist at the wrong location — For the Navy Method, measure waist at the navel (not the narrowest point). Consistency matters most.
• Expecting exact results — All non-laboratory methods have ±3–5% error margins. Track trends over time rather than treating any single measurement as absolute.
• Targeting extremely low body fat — Below essential fat levels is dangerous. Even very lean athletes maintain well above minimum essential fat.

Frequently Asked Questions

What is the most accurate way to measure body fat?

DEXA scan (±1% accuracy) is considered the gold standard. Hydrostatic (underwater) weighing is also highly accurate. BOD POD uses air displacement. Skinfold calipers (with trained technician) are ±3–4%. All are more accurate than circumference methods.

How quickly can I reduce body fat?

A safe rate is 0.5–1% body fat reduction per month. Aggressive deficits (too fast) risk losing muscle mass along with fat. Combine a calorie deficit with resistance training to preserve lean muscle.

Should I track weight or body fat percentage?

Both. Scale weight can be misleading — you may gain muscle while losing fat, showing no scale change despite significant body composition improvement. Tracking both weight and estimated body fat tells the full story.

Conclusion

Body fat percentage gives you the composition insight that BMI alone can't. Use this calculator regularly (every 4–6 weeks) to track body composition changes — especially if you're strength training where muscle gain may mask fat loss on the scale.

Related: BMI Calculator | Lean Body Mass Calculator | BMR Calculator | Calorie Calculator