Body fat percentage tells you something BMI cannot: how much of your weight is fat and how much is everything else. The US Navy circumference method needs only a tape measure, and while it is less precise than a DEXA scan, it tracks change over time well — which is what actually matters.
Typically within three to four percentage points of a DEXA scan for most people, with larger errors at the extremes. Its real strength is consistency: measured the same way each time, it tracks change reliably.
Men measure at the navel; women measure at the narrowest point of the torso. Using the wrong landmark is the biggest source of error in the whole method.
Commonly cited ranges are roughly 10–20% for men and 18–28% for women, with athletes below and essential fat minimums around 3% and 12% respectively. Ranges vary by age and source.
Hydration, meals, time of day, and tape tension all shift the numbers. Measure first thing in the morning, before eating, for the most comparable results.
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