Body Fat Calculator
Estimate body fat % using the US Navy circumference method — the most accessible non-lab measurement.
Measure neck at narrowest point; waist at navel; hips at widest point.
How the Navy method works
The US Navy circumference method was developed to estimate body fat percentage using simple tape measurements. It uses height, neck, waist (and hip for females) to produce a body density estimate, which is converted to body fat percentage.
While not as accurate as DEXA scans or hydrostatic weighing, the Navy method has a standard error of ~3–4% and is useful for tracking changes over time. Take measurements in the morning before eating, relaxed (not flexed), and use the same tape for consistency.
Body fat calculator — FAQ
For men, 10–20% is considered fitness range, with 6–13% being athletic and 21–24% acceptable. For women, 18–28% is fitness range, 14–20% athletic, and 25–31% acceptable. Essential fat (the minimum for health) is 2–5% for men and 10–13% for women. Body fat below essential fat levels is dangerous and associated with organ damage and hormonal disruption.
Monthly is the recommended frequency for most people. Daily measurements are too noisy — body fat estimates fluctuate based on hydration, food volume, and measurement error. Measuring monthly under consistent conditions (same time of day, same tape measure) gives you reliable trend data without obsessing over day-to-day noise.