Body Fat Calculator

What does this Body Fat Calculator do?

This calculator estimates body fat percentage using the U.S. Navy circumference method — a tape-measure-based technique developed by the US Navy as a practical field alternative to lab equipment like DEXA scans or hydrostatic weighing.

The formula

The Navy method uses logarithms of your waist, neck, and (for women) hip measurements along with height. It's more complex than a simple ratio, which is part of why it correlates reasonably well with more expensive lab methods despite only requiring a tape measure.

Step-by-step example

For a man who is 175 cm tall with an 85 cm waist and 38 cm neck, the formula uses log₁₀ of the difference between waist and neck measurements, along with log₁₀ of height, to estimate body fat percentage — typically landing somewhere in the high teens to low twenties for an average-build adult male.

Tips & common mistakes

• Measurement technique matters a lot — measure at the same time of day, same tension on the tape, and the exact same landmark each time for consistent tracking.
• This method is best used to track trends over weeks and months, not as a one-time precise number — a single measurement can be off by a few percentage points.
• Women need an additional hip measurement that men don't, since fat distribution patterns differ meaningfully by sex.

Body fat percentage ranges

General reference ranges (which vary somewhat by source and age) put "athletic" body fat around 6–13% for men and 14–20% for women, "fit" around 14–17% for men and 21–24% for women, and "average" around 18–24% for men and 25–31% for women — though individual context, age, and genetics all play a role in what's healthy for a given person.

Other ways to measure body fat

Beyond the Navy tape-measure method, other common approaches include skinfold calipers (pinching and measuring skin thickness at several body sites), bioelectrical impedance scales (which estimate body composition from a small electrical signal), and DEXA scans (a precise medical imaging method). Each trades off cost and accessibility against accuracy.

Why the Navy method uses circumference rather than weight

Unlike BMI, which uses only height and weight, the Navy method's circumference-based approach captures information about where mass is actually distributed on the body — which correlates better with body fat than weight and height alone, since two people of identical height and weight can carry very different amounts of visceral (abdominal) fat.

Body fat and health risk, particularly abdominal fat

Research consistently links abdominal (visceral) fat specifically — more than overall body fat percentage — to increased cardiovascular and metabolic disease risk, which is part of why waist circumference is often tracked as its own independent health metric alongside body fat percentage.

Consistency in measurement technique

For tracking body fat percentage over time, consistency matters more than any single reading's absolute precision — measure at the same time of day (ideally morning, before eating), with the same tape tension, and at the same anatomical landmarks each time, so that any change you observe reflects a real change in your body rather than measurement noise.

Frequently asked questions