Body Fat Percentage Estimator
Estimate your body fat % using the U.S. Navy circumference method — fast, free, and accurate.
Uses the U.S. Navy circumference method. Measurements should be taken at the widest point.
How to Use This Body Fat Percentage Calculator
Select your gender, choose your preferred unit system (imperial or metric), then enter your height, weight, neck circumference, waist circumference — and hip circumference if you're female. Adjust your age with the slider or type it in directly. Hit Calculate Body Fat % to see your result, category classification, and a color-coded zone chart showing where you fall.
Why This Matters
Body fat percentage is one of the most meaningful indicators of physical fitness and metabolic health — more informative than weight alone or even BMI. Two people can weigh exactly the same but have dramatically different body compositions. A 180 lb man at 12% body fat (competitive athlete territory) has 21.6 lbs of fat and 158.4 lbs of lean mass, while another 180 lb man at 28% carries 50.4 lbs of fat. The health implications are vastly different.
Excess body fat — particularly visceral fat stored around the abdomen — is associated with increased risk of type 2 diabetes, cardiovascular disease, high blood pressure, and joint stress. The American Council on Exercise classifies 25–31% as "average" for men in their 30s and 32–38% for women, but fitness-focused individuals typically target the 14–24% range for men and 21–33% for women.
Tracking body fat percentage over months gives you a true picture of whether you're gaining muscle, losing fat, or just shifting water weight — something the bathroom scale simply cannot tell you.
How It's Calculated
This tool uses the U.S. Navy Circumference Method, developed by Hodgdon and Beckett in 1984 and still used by the U.S. military for fitness assessments. It requires only a tape measure and is accurate to within ±3–4% of DEXA scan results for most people.
For Men:
BF% = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
For Women:
BF% = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
All measurements are in inches. Lean body mass is then calculated as: LBM = Weight × (1 − BF%/100), and fat mass as Weight − LBM.
Tips & Common Mistakes
- Measure consistently: Always measure at the same time of day (morning, before eating) and use the same spots. Waist should be measured at the navel level, not the narrowest point.
- Don't suck in your stomach: Waist measurement should reflect your relaxed, natural circumference — not a flexed or sucked-in position.
- Use a flexible tape measure: A rigid ruler or estimating with string introduces significant error. A proper fabric tape measure costs under $3.
- Neck measurement: Measure just below the larynx (Adam's apple) and keep the tape horizontal. Don't compress the skin.
- Track trends, not single readings: A single measurement has inherent error. Measure weekly and look at the 4-week trend to understand your true trajectory.
Frequently Asked Questions
How accurate is the Navy method compared to DEXA or hydrostatic weighing?
The U.S. Navy method is accurate to approximately ±3–4 percentage points for most adults when measurements are taken correctly. DEXA scans are considered the gold standard with ±1–2% accuracy, but cost $50–200 per session. The Navy method provides an excellent free alternative for regular tracking at home.
What is a healthy body fat percentage for my age?
Healthy ranges increase slightly with age. For men, 8–19% is generally considered fit at ages 20–39, while 11–21% is normal at 40–59. For women, 21–32% is fit at 20–39 and 23–33% at 40–59. Athletes often maintain lower percentages, but essential fat (3–5% for men, 10–13% for women) is required for organ function.
Can I use this for children or teenagers?
No — this calculator is designed for adults aged 18 and over. The U.S. Navy formula was validated on adult populations only. Children and teenagers have different body composition norms and require age-specific methods such as skinfold calipers interpreted with pediatric charts.
Why is my result different from what a body composition scale shows?
Bioelectrical impedance scales (common bathroom scales with BF% reading) are affected significantly by hydration levels, food intake, and skin temperature — they can swing 3–8% in a single day. The Navy method, while not perfect, is more stable day-to-day because tape measurements don't fluctuate as dramatically with hydration.