Why does the formula need a logarithm?

The relationship between circumference measurements and actual body fat (as validated against underwater weighing, the original gold-standard reference) isn't linear -- log-scaling the circumference and height terms produced the best statistical fit in the Navy's original research, which is why the constants and log terms are specific and shouldn't be simplified.

Why do women need a hip measurement but men don't?

Body fat distribution differs by sex -- women tend to carry proportionally more fat around the hips, so the female formula includes hip circumference to keep the estimate accurate, while the male formula relies on waist and neck alone.

How accurate is this compared to a DEXA scan or hydrostatic weighing?

The U.S. Navy method typically comes within about 3–4 percentage points of more precise lab methods like DEXA for most people, which is accurate enough for tracking trends over time, but it can be less reliable for people with atypical fat distribution or very high or low muscle mass.

What if my waist measurement is smaller than my neck?

The formula requires waist (plus hip, for women) to exceed neck circumference, since the log of a zero or negative number is undefined -- this calculator flags that case explicitly rather than showing a nonsensical result.

Body Fat % Calculator

Uses the U.S. Navy method — a tape-measure formula, not a scale or skinfold caliper reading. Measure your waist and neck at their most natural points for the most accurate result.

How Body Fat % Calculator Works

The U.S. Navy method estimates body fat percentage from a handful of circumference measurements instead of a scale, skinfold calipers, or a DEXA scan. It was developed by the U.S. Navy as a fast, low-equipment way to estimate body composition for fitness standards, and remains one of the most widely used tape-measure methods because it needs nothing more than a flexible measuring tape.

Formula & Method

For men: Body Fat % = 495 / (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450. For women, hip circumference is added to the mix: Body Fat % = 495 / (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450. All measurements are converted to inches before being plugged in, since that's the unit system the original Navy formula was derived in, even though this calculator accepts centimeters.

Worked Example

For a man with height 170cm (66.9in), neck 38cm (15.0in), and waist 85cm (33.5in): the waist-minus-neck term is 18.5in, giving a body fat estimate of about 11.4% -- landing in the "Athletes" range (6–14%), just above the essential-fat floor.

Frequently Asked Questions

Why does the formula need a logarithm?: The relationship between circumference measurements and actual body fat (as validated against underwater weighing, the original gold-standard reference) isn't linear -- log-scaling the circumference and height terms produced the best statistical fit in the Navy's original research, which is why the constants and log terms are specific and shouldn't be simplified.
Why do women need a hip measurement but men don't?: Body fat distribution differs by sex -- women tend to carry proportionally more fat around the hips, so the female formula includes hip circumference to keep the estimate accurate, while the male formula relies on waist and neck alone.
How accurate is this compared to a DEXA scan or hydrostatic weighing?: The U.S. Navy method typically comes within about 3–4 percentage points of more precise lab methods like DEXA for most people, which is accurate enough for tracking trends over time, but it can be less reliable for people with atypical fat distribution or very high or low muscle mass.
What if my waist measurement is smaller than my neck?: The formula requires waist (plus hip, for women) to exceed neck circumference, since the log of a zero or negative number is undefined -- this calculator flags that case explicitly rather than showing a nonsensical result.

Sex

Height (cm)

Neck Circumference (cm)

Waist Circumference (cm)

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