Body Fat Percentage: What the Tape Measure Can and Cannot See

Quick answer: The most practical field estimate is the US Navy circumference method: for a man, %BF = 495 ÷ (1.0324 − 0.19077×log₁₀(waist − neck) + 0.15456×log₁₀(height)) − 450 with measurements in cm. It needs only a tape measure, and it carries an honest error band of roughly ±3–4% against lab methods.

The US Navy method, worked

Example — a man 180 cm tall, neck 38 cm, waist 84 cm: waist − neck = 46 cm; log₁₀(46) = 1.6628; log₁₀(180) = 2.2553. Denominator = 1.0324 − 0.19077×1.6628 + 0.15456×2.2553 = 1.0324 − 0.3172 + 0.3486 = 1.0638. %BF = 495 ÷ 1.0638 − 450 = 15.2%. Women use the same constants with hips instead and a different intercept — the calculator implements both.

Body fat vs BMI: different questions

A muscular person can be "overweight" by BMI at 12% body fat; a sedentary person can be "normal" by BMI at 28% body fat. The two numbers answer different questions and are most useful together.

Every method has an error band

	BMI	Body-fat %
Inputs	Weight and height only	Circumferences (or calipers/DEXA)
Sees muscle vs fat?	No	Partially — fat distribution matters
Typical use	Population screening	Body-composition tracking
Common ranges (men)	"Normal" 18.5–24.9	Athletes 6–13%, fitness 14–17%, average 18–24%

DEXA scans are treated as reference but still vary between machines; calipers depend on the measurer's skill; the Navy formula averages about ±3–4% error. That is fine for tracking change — if your estimate falls from 24% to 20% under a consistent method, real fat was likely lost even if the absolute number is off. It is not fine for diagnosing anything.

Limitations: circumference formulas were developed on specific populations and lose accuracy at very high or very low body fat, and measurement technique (tape tension, time of day, measurement sites) moves results by whole percentage points. Track trends with the same method, same conditions.

Try the calculators

Frequently asked questions

How do I measure for the Navy method?

Use a flexible tape: measure the neck below the larynx, the waist at the navel (men) or at the narrowest point plus hips at the widest (women), keep the tape snug but not compressing skin, and measure at the same time of day — morning, before eating, is standard.

What body fat percentage is healthy?

Ranges shift by source, but commonly cited bands are roughly 10–20% for men and 18–28% for women in normal healthy adults, with athletes lower. Essential fat — needed for physiological function — is around 3% for men and 12% for women, so lower is not better.

Is the Navy formula accurate?

Compared against DEXA it typically lands within ±3–4% for most people, which is comparable to consumer bioimpedance scales and better than nothing. Its real value is tracking change under a consistent technique.

Why do different calculators give me different numbers?

Different formulas (Navy, Covert Bailey, YMCA) use different measurement sites and coefficients, and each carries its own error band. Pick one method and stay with it so your trend line means something.

About this guide: Written and maintained by CalcProMaster’s developer — an independent site, not a licensed financial advisor or medical professional. Every worked example below was computed by hand and cross-checked with the linked calculator; our editorial policy explains how content is written, tested and corrected.