Body Fat Calculator
Estimate body fat percentage using the U.S. Navy tape-measure method.
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How the Navy body fat method works
This calculator uses the circumference-based formula developed for the U.S. Navy in the early 1980s, chosen because it needs nothing more than a flexible tape measure and gives results reasonably close to underwater weighing for most body types. Men need three measurements — height, neck, and waist — while women add a hip measurement, because fat distribution differs between the sexes.
For men, the formula is: %BF = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450. For women it becomes: %BF = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450, with all measurements in centimeters. Small errors in where you place the tape can shift the result noticeably, so measure at the same time of day, without clothing compressing the area, and take the waist reading at the narrowest point (or at the navel if there's no clear narrowing).
Once you have a percentage, this calculator sorts it into ranges commonly used in fitness coaching — essential fat, athletic, fitness, average, and obese — which differ slightly by gender because women naturally carry more essential fat for reproductive health. If you also enter your weight, the tool splits it into fat mass and lean mass, useful for tracking body recomposition over time rather than just the scale number. Re-measure every two to four weeks rather than daily; short-term fluctuations from water retention, food, and hydration can outweigh real changes in fat.
Frequently asked questions
How accurate is the Navy tape-measure method? It's typically within a few percentage points of more expensive methods like DEXA scans for most body types, which is why the military and many gyms use it as a quick field test.
Why does the formula need neck and waist, not just weight? Weight alone can't distinguish fat from muscle. Circumference measurements at the neck, waist, and (for women) hip correlate with body fat percentage regardless of how much someone weighs on a scale.
What counts as a "good" body fat percentage? Ranges vary by goal and sex, but roughly 10–20% for men and 18–28% for women is considered a healthy, sustainable range for most non-athletes — see the category breakdown above the calculator for the full scale.
Worked example
Using the U.S. Navy method for a man 180 cm tall with a 90 cm waist and 38 cm neck, the formula typically returns a result around 18–19%, which sits in the “acceptable” to “fitness” range for men.
Why does the calculator ask for a tape measurement instead of just weight? Two people can weigh the same but carry very different amounts of muscle versus fat — waist, neck (and hip, for women) measurements correlate much more closely with actual body-fat percentage than weight alone.
How accurate is the tape-measurement method compared to a DEXA scan? It's typically within 3–4 percentage points of a DEXA scan for most people, which is accurate enough for tracking trends over time, though not precise enough for clinical use.