Body Fat Calculator (US Navy Method)
Measuring Body Fat With Just a Tape Measure
Most methods of measuring body fat require expensive equipment or lab testing. The US Navy method needs nothing but a tape measure and a few minutes — and it's accurate enough for tracking progress over time, which is what matters most in practice.
How to Use This Calculator
Select your gender, then enter your height, total body weight, waist circumference (at the navel, standing relaxed), and neck circumference (just below the larynx). Women also enter hip circumference at the widest point. Consistency in measurement technique is crucial — measure the same way each time for reliable comparisons.
Measurement Tips for Accuracy
- Waist — measure at the navel, not at the narrowest point. Stand relaxed, exhale normally, don't suck in. The tape should be snug but not compressing skin.
- Neck — measure just below the larynx (Adam's apple), tilting the tape slightly downward at the front. Keep the tape perpendicular to your spine.
- Hips (women only) — measure at the widest point of the hips and buttocks, usually 7–9 inches below the navel. Stand with feet together.
- Consistency — measure at the same time of day (morning before eating is most consistent), use the same tape, and take 2–3 measurements and average them.
How the US Navy Formula Works
The US Navy method was developed in the 1980s and uses circumference measurements to estimate body fat percentage. The formulas are:
Women: BF% = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
All measurements in inches. The formula exploits the relationship between circumference ratios and fat distribution patterns — wider waist relative to neck (and hips for women) predicts higher body fat.
Real-World Example
Using the calculator's defaults — male, 70" height, 185 lbs, 36" waist, 16" neck:
- Body fat percentage: ~19.4%
- Category: Average (18–24%)
- Fat mass: ~35.9 lbs
- Lean mass: ~149.1 lbs
To reach 15% body fat (fitness category), this person would need to lose approximately 8–9 lbs of fat while maintaining lean mass — achievable over 2–3 months with a moderate calorie deficit and adequate protein.
Body Fat Categories
Men:
- 2–5% — Essential fat (minimum for bodily functions)
- 6–13% — Athletic
- 14–17% — Fitness
- 18–24% — Average
- 25%+ — Obese
Women:
- 10–13% — Essential fat
- 14–20% — Athletic
- 21–24% — Fitness
- 25–31% — Average
- 32%+ — Obese
Women naturally carry more body fat than men at equivalent fitness levels — this is biological, not a health concern.
Body Fat vs. BMI — Why Body Fat Is More Informative
BMI uses only height and weight — it can't distinguish between fat and muscle. Two people with identical BMIs can have very different body compositions. Body fat percentage is a direct measure of how much of your body weight is fat tissue, making it far more useful for assessing health and tracking fitness progress. Our BMI calculator is useful for population-level screening; body fat percentage tells you more about what's actually happening with your body composition.
Frequently Asked Questions
How accurate is the US Navy method?
Studies show the US Navy method is accurate to within ±3–4% compared to DEXA scanning (the gold standard) for most people. It's less accurate for very lean or very obese individuals where circumference patterns diverge from typical fat distribution. For tracking progress over time, the exact number matters less than consistency — the same technique applied regularly gives you reliable trends.
What's the most accurate way to measure body fat?
DEXA (Dual-Energy X-ray Absorptiometry) scanning is the clinical gold standard — it differentiates bone, fat, and lean tissue precisely. Hydrostatic weighing and Bod Pod testing are also highly accurate. Skinfold calipers with a trained technician are reasonably accurate. Bioelectrical impedance (home scales and handheld devices) is the least accurate and is significantly affected by hydration levels.
How often should I measure?
Once every 4–6 weeks is enough to track meaningful change. Body fat doesn't shift week to week in measurable amounts — taking measurements too frequently adds noise and can cause unnecessary frustration. Weight can fluctuate by several pounds daily due to water and food; body fat changes much more slowly.
What body fat percentage is healthy?
For general health, the fitness and average ranges are both considered healthy for most adults. Very low body fat (below essential fat levels) impairs hormone function, immune response, and organ protection. Very high body fat increases risk of metabolic disease, cardiovascular issues, and joint strain. The fitness category is a reasonable target for most active adults.
How do I reduce body fat percentage?
A calorie deficit combined with adequate protein and strength training is the most effective approach — it preferentially reduces fat while preserving or building lean mass. Use our calorie calculator to find your deficit target and our macro calculator to set a high-protein split that protects muscle during the cut.