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Body Fat Percentage Calculator

The US Navy tape method — what BMI cannot tell you.

Inputs
Sex
cm
cm

Measured just below the larynx.

cm

At the navel for men, at the narrowest point for women.

cm

Widest point. Required for women only.

Body fat
23.5%
EssentialAthleteFitnessAverageHigh
Category
Average
US Navy (metric): male 86.010·log₁₀(waist − neck) − 70.041·log₁₀(height) + 36.76

The tape method carries roughly three to four percentage points of error against a DEXA scan.

Every tool runs entirely in your browser. Your files are never uploaded to a server.

The US Navy method estimates body fat from a few tape measurements rather than weight. Because it measures girth instead of mass, it distinguishes muscle from fat in a way BMI cannot. Expect roughly three to four points of error.

How to use the Body Fat Calculator

  1. Measure your neck and waist. Use a soft tape. Neck just below the larynx, waist at the navel for men or the narrowest point for women.
  2. Add hip measurement if female. Women also need hip circumference at the widest point; the formula requires it.
  3. Enter the numbers. Your estimated body fat percentage and fitness category appear immediately.

About body fat percentage

The circumference method was developed by the US Navy so that body composition could be assessed at scale without laboratory equipment, and it remains one of the better field estimates available. It works because fat distribution follows reasonably predictable patterns: the difference between neck and waist girth, scaled against height, correlates well with total fat mass across large populations. That population-level basis is also where its error comes from. Anyone whose fat distribution is unusual will be misread, and the formula makes no allowance for frame size or ethnicity, both of which shift the relationship. Measurement technique matters more than most people expect. Pulling the tape tight, measuring over clothing, or taking the waist at a different landmark between sessions can move the result by several percentage points on its own, which is easily mistaken for real change. For tracking progress, measure at the same time of day under the same conditions and pay attention to the trend across weeks rather than any single reading. For a genuinely precise figure, DEXA or hydrostatic weighing remain the reference methods.

Frequently asked questions

How accurate is the US Navy method?
It typically lands within three to four percentage points of a DEXA scan. That is good enough to track change over time, but not precise enough to treat as an exact figure.
Why is this better than BMI?
BMI uses only height and weight, so it cannot separate muscle from fat. The tape method measures where fat is actually stored, which is why muscular people score very differently on the two.
What is a healthy body fat percentage?
Broadly, 14 to 24 percent for men and 21 to 31 percent for women is considered acceptable. Athletes sit lower. Below the essential fat threshold is a health risk.
Is my data sent anywhere?
No. Every measurement stays in your browser and is never transmitted or stored.

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