This calculator estimates your body fat percentage with a tape measure, using the US Navy circumference method — the same technique used for military fitness assessments. You only need your height and a few circumference measurements.
Body Fat Calculator (US Navy Method)
Estimate only — not medical advice.
How to Measure Correctly
- Neck: around the middle of the neck, just below the Adam’s apple, tape level.
- Waist: at the navel (belly button), standing relaxed — do not pull your stomach in.
- Hips (women only): around the widest point of the hips and glutes.
- Measure in the morning, on bare skin, and take each measurement twice. Average the two readings.
How the Navy Method Works
The US Navy formulas estimate body fat from the difference between waist and neck circumferences (plus hips for women), adjusted for height, using logarithmic equations developed from body-composition research. For men: BF% = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76, with all measurements in inches.
Worked Example
A man, 178 cm tall, neck 38 cm, waist 86 cm: the formula gives a body fat estimate of about 17% — in the “Fitness” range (14–17% for men).
Body Fat Categories
- Men: Athletes 6–13% · Fitness 14–17% · Average 18–24% · Obese 25%+
- Women: Athletes 14–20% · Fitness 21–24% · Average 25–31% · Obese 32%+
Frequently Asked Questions
How accurate is the Navy tape method?
When measurements are taken carefully, it typically lands within about 3–4% of lab methods such as DEXA — good enough to track changes over time.
Why does the calculator ask for neck size?
The neck measurement separates lean frame size from fat stored around the waist, which is what makes the formula work.
How often should I measure?
Every 2–4 weeks, at the same time of day. Day-to-day changes are water and measurement noise, not fat.
What is a healthy body fat percentage?
Roughly 10–20% for men and 18–28% for women covers the healthy-to-fit range for most adults.