Body Fat Calculator

Body fat percentage is the share of your total body weight that is fat, as opposed to muscle, bone, organs, and water. It is often more useful than weight or BMI alone, because two people at the same weight can carry very different amounts of fat and muscle. This calculator uses the U.S. Navy circumference method, which estimates body fat from a few tape measurements — no calipers, scales, or scans required.

The method works because body-fat distribution follows fairly predictable patterns relative to height and girth. For men it uses height, neck, and waist; for women it adds hip circumference, since fat is distributed differently. Accurate measuring matters more than anything else here: use a flexible tape, keep it level, and don't compress the skin. A small error in the tape reading moves the result more than you might expect.

Because it is an estimate from external measurements, treat the number as a ballpark that is most useful for tracking change over time. If your measurements are consistent, watching the figure move over weeks and months is more informative than any single reading. For a definitive assessment, laboratory methods such as a DEXA scan remain the reference standard.

The Navy method is most accurate for adults with a typical build who measure carefully and consistently. Because it relies on the usual relationship between girth and body fat, it performs best for people near the middle of the range and is especially good at tracking change over time when your technique stays the same.

It is least accurate at the extremes — very lean athletes and people with very high body fat — and for anyone whose fat is distributed atypically, since the equation assumes an average pattern. Inconsistent tape placement or tension is the most common real-world source of error, often larger than the method's own ±3–4% margin. If you need a precise, one-time body-composition figure rather than a trend, a DEXA scan or hydrostatic weighing is the appropriate tool.

Formula. The Navy method applies a logarithmic equation to your circumference measurements and height. For men, %BF = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450; the women's equation uses waist + hip − neck and its own coefficients. All measurements are taken in centimetres (the calculator converts from inches for you).

Source. The equations come from Hodgdon and Beckett's 1984 study for the Naval Health Research Center and were adopted by the U.S. Navy for fitness assessment. They are widely cited as a reasonably accurate, equipment-free way to estimate body fat.

Confidence. We label this moderate confidence. Validation studies show roughly ±3–4% error against DEXA-scan results, so the estimate is accurate to within a few percentage points rather than being clinically exact. It is a practical screening and tracking tool, not a substitute for laboratory body-composition testing.