Body Fat Calculator
Estimate body fat percentage using the U.S. Navy method — just a tape measure, your height, and a few body circumferences.
What is Body Fat Calculator?
The body fat calculator estimates your percentage of body fat from a few simple tape-measure readings using the U.S. Navy circumference method. It is the same protocol the Navy uses for fitness-standard screening.
Body fat percentage is a better indicator of health and fitness than BMI because it separates lean mass from fat. Two people with identical BMI can have very different body compositions.
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 are in inches. Results are typically within ±3–4% of a DEXA scan.
Worked example
A man 69 in tall, neck 15 in, waist 34 in:
- waist − neck = 19
- BF% = 86.010 × log(19) − 70.041 × log(69) + 36.76
- ≈ 86.010 × 1.279 − 70.041 × 1.839 + 36.76
- ≈ 17.8% body fat (Fitness range)
How to use this calculator
- Measure your neck just below the larynx (Adam's apple). Keep the tape level; do not flex.
- Measure your waist horizontally at the navel. Exhale normally — do not suck in.
- Women only: measure your hip at the widest point.
- Pick units that match your tape and enter the numbers.
Tip: use a soft cloth tape, keep it snug but not compressing, and measure 2–3 times and average.
Frequently asked questions
How does this compare to a DEXA scan?
DEXA (dual-energy X-ray absorptiometry) is the gold standard and typically reads within ±1–2% of true body fat. The Navy method is usually within 3–4% of DEXA for most people. Skinfold calipers and bioelectric impedance scales are often less accurate than the Navy method, not more.
What body fat percentage is healthy?
The American Council on Exercise lists these ranges: Men — 6–13% athletes, 14–17% fitness, 18–24% average, 25%+ obese. Women — 14–20% athletes, 21–24% fitness, 25–31% average, 32%+ obese. Very low body fat (below ~5% men, ~12% women) can impair health.
Why is the formula different for men and women?
Women store more essential fat in the hips, breasts, and thighs, so the female formula adds hip circumference. Men store fat predominantly in the abdominal region, which the waist measurement captures on its own.
How often should I remeasure?
Every 2–4 weeks is plenty. Day-to-day changes in hydration and food in the GI tract can swing the waist measurement by up to an inch, which is ±2% body fat of noise.