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Body Fat Percentage Calculator. From a tape measure.

Estimated body fat from circumference measurements, using the U.S. Navy method — no calipers needed.

Live calculation

What's your body fat?

Sex
in
in
in

Measure neck just below the larynx, waist at the navel, and (for women) hip at its widest point — snug but not compressed.

Body fat percentage 17.5%
Category
Fitness
Typical range
14–18%

waist − neck = 19.0 in
%BF = 86.010 × log₁₀(19.0) − 70.041 × log₁₀(70.0) + 36.76 = 17.5%

Your figures are kept on this device only.

How it works

The U.S. Navy method estimates body fat from a small set of circumference measurements instead of skinfold calipers or lab equipment, using a regression formula developed by Hodgdon and Beckett (1984). It's not as precise as a DEXA scan or hydrostatic weighing, but it's inexpensive, repeatable, and reasonably accurate for tracking change over time.

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 go into this formula in inches — when your locale is set to metric, this calculator converts centimetre entries to inches internally before applying it, so the result is the same regardless of which units you typed in.

Worked example

A man, height 70 in, neck 15 in, waist 34 in.

Step by step
  1. waist − neck = 34 − 15 = 19 in.
  2. 86.010 × log₁₀(19) = 86.010 × 1.279 = 109.99.
  3. 70.041 × log₁₀(70) = 70.041 × 1.845 = 129.23.
  4. %BF = 109.99 − 129.23 + 36.76 = 17.5%.

An estimated 17.5% body fat, which falls in the Fitness category (14–18%) for men.

Common questions

How accurate is the Navy method?

Studies generally show it within about 3–4 percentage points of DEXA scan results for most body types, though it becomes less reliable at the extremes (very lean or very high body fat). It's best used consistently over time to track trend, rather than trusted as an exact one-off figure.

Why does the formula need waist minus neck?

Waist circumference reflects both fat and frame size; subtracting neck circumference (a measurement that barely changes with body fat) helps cancel out frame size, leaving a value that tracks fat more specifically. It's a simple but effective piece of the original regression's design.

Why do men and women use different formulas?

Fat distribution differs by sex — women typically carry more fat around the hips, which is why the women's formula adds a hip measurement the men's formula doesn't use. The category bands are also different: essential fat alone is higher in women than men for basic physiological reasons.