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Health & Body
Body Fat Calculator — U.S. Navy Method (Body Fat Percentage)
Estimate body fat percentage from a tape measure — no calipers, scales or gym needed
Your weight on the bathroom scale tells you almost nothing about your body composition — two people at the same height and 180 lb can carry wildly different amounts of fat and muscle. The body fat percentage is what actually matters for fitness, and you can estimate it at home with nothing but a flexible tape measure using the U.S. Navy method (also called the circumference or "tape" method).
The Navy formula uses your height plus a few girth measurements, all in inches. For men it needs neck and waist; for women it adds the hip. The math is a pair of log-based equations:
• 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
Worked example (man): height 70 in, neck 15 in, waist 34 in. waist − neck = 19, log₁₀(19) = 1.2788, log₁₀(70) = 1.8451. BF% = 86.010 × 1.2788 − 70.041 × 1.8451 + 36.76 = 17.5% — squarely in the "fitness" range.
How to measure: stand relaxed, exhale normally, and keep the tape snug but not compressing the skin. Measure the neck just below the larynx (Adam's apple), the waist at the navel for men (at the narrowest point for women), and the hip at the widest point for women. Always round to the nearest half inch and remeasure twice.
The most common mistake is sucking in your stomach or pulling the tape tight on the waist — that shaves inches off and makes the result read artificially lean. The opposite, measuring over a thick sweater, inflates it. Consistency matters more than perfection: measure the same way each time so you can track the trend.
A quick reality check on accuracy: the Navy method is typically within about 3–4 percentage points of a DEXA or hydrostatic scan for most people, but it can drift several points for very muscular or very lean individuals, since the tape can't distinguish a hard midsection from a soft one. Use the result as a fitness-tracking estimate, not a medical diagnosis or a substitute for a clinical body-composition scan. For body-composition decisions tied to health, talk with a doctor or a registered dietitian.
📖 See also: Body Fat Percentage: How to Measure It at Home
Calculator
Fill in the fields and click "Calculate" for instant results.
📰 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 • Fat mass (lb) = weight × BF% / 100 • Lean mass (lb) = weight − fat mass • All circumferences and height are in inches
📰 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 • Fat mass (lb) = weight × BF% / 100 • Lean mass (lb) = weight − fat mass • All circumferences and height are in inches
🧪 Worked examples
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Example 2
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Example 3
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Example 4
⚠️ Common mistakes
- Sucking in your stomach or pulling the tape tight, which under-reads the waist.
- Measuring over clothing or a thick waistband instead of bare skin.
- Women forgetting the hip measurement — the female formula requires it.
- Mixing units (entering centimeters into inch fields) or rounding too aggressively.
💡 Tips
- Measure first thing in the morning, before eating, for a consistent baseline.
- Keep the tape level and snug — not biting into the skin — and remeasure twice.
- Track the trend over weeks; a single reading matters far less than the direction.
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❓ Frequently asked questions
How accurate is the U.S. Navy body fat calculator?
For most people it lands within about 3–4 percentage points of a DEXA or hydrostatic (underwater) scan. It's less reliable for very muscular or very lean bodies, but it's free, fast and good for tracking trends over time.
Where exactly do I measure my waist and neck?
Measure the neck just below the Adam's apple. For men, measure the waist at the navel; for women, at the narrowest point. Keep the tape snug, exhale normally, and don't suck in your stomach.
Why does the women's formula need a hip measurement?
Women carry more body fat around the hips, so the female equation adds the hip circumference to the waist and subtracts the neck. Without it the math can't be solved — the hip field is required for women.
What is a healthy body fat percentage for men and women?
Per ACE guidelines, men: 6–13% athlete, 14–17% fitness, 18–24% average, 25%+ obese. Women run higher: 14–20% athlete, 21–24% fitness, 25–31% average, 32%+ obese, because of greater essential fat needs.
What's the difference between fat mass and lean mass?
Fat mass is your weight times your body fat percentage. Lean mass is everything else — muscle, bone, organs and water. Enter your weight and the calculator splits the two for you in pounds.
Do I need a body fat scale or calipers to use this?
No. The Navy method needs only a flexible tape measure and your height. That's its main advantage over skinfold calipers (which require skill) or smart scales (which use bioelectrical impedance).
How is this different from BMI?
BMI uses only height and weight, so a muscular person can be flagged 'overweight' despite low fat. Body fat percentage measures actual fat, making it a better fitness gauge — though still an estimate, not a diagnosis.
Should I measure in inches or centimeters?
This calculator is set up for inches, the standard U.S. unit. Enter height, neck, waist and hip all in inches. Rounding each to the nearest half inch is fine for a reliable estimate.
Can I rely on this for medical decisions?
No. This is an informational estimate for general fitness tracking, not medical advice or a diagnosis. For health decisions tied to body composition, consult a doctor or registered dietitian.