Body Fat Calculator
Estimate body-fat percentage (U.S. Navy method).
Input sheet
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Body-fat percentage tells you what share of your weight is fat versus everything else — a far more useful fitness gauge than the scale or BMI. This tool uses the U.S. Navy tape method, which needs only a measuring tape and a few minutes.
How it works
Uses neck, waist (and hip for women) circumferences with height. An estimate — calipers or DEXA are more precise.
The Navy method estimates body fat from circumferences: neck and waist for men, plus hip for women, combined with height. Those sites correlate well with overall fat distribution, which is why the formula works without calipers.
Measure on bare skin with the tape snug but not compressing — waist at the navel, neck just below the larynx, hips at the widest point. Small measurement errors move the result by a percentage point or more, so measure twice and average.
Men: % fat = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76. Women: % fat = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387 (all inches).
Worked examples
A man 5'10" (70 in) with a 34" waist and 15" neck. → About 17.5% body fat — the fitness range.
86.010 × log₁₀(19) − 70.041 × log₁₀(70) + 36.76 ≈ 110.0 − 129.2 + 36.8 ≈ 17.5%.
A woman 5'6" with a 30" waist, 40" hips, 13" neck. → Roughly 30% body fat — the average range.
Plugging waist + hip − neck = 57 in into the women's formula lands near 30%.
Tips & gotchas
- Measure first thing in the morning before eating or drinking, when bloating is lowest and readings are most consistent.
- Keep the tape level and parallel to the floor — a tilted waist measurement is the most common source of error.
- Re-measure every two to four weeks under the same conditions; trends matter more than any single number.
- For a precise reading, calipers, a body-fat scale, or a DEXA scan beat the tape method — but the tape is free and trends reliably.
FAQ
How accurate is the Navy tape method?
It lands within a few percentage points for most people and tracks changes well over time. It's less precise than DEXA but far cheaper and accurate enough for everyday goals.
What's a healthy body-fat percentage?
Roughly 10-20% for men and 18-28% for women is a common healthy range, with athletes lower. Essential fat sits around 3-5% for men and 10-13% for women.
Why does it need my neck and waist instead of weighing me?
Fat distribution at the waist and neck predicts overall body fat better than weight does. The circumferences let the formula estimate composition without any scale at all.
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