One-Site vs Legacy 3-Site: Worked Body Fat Examples

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By Bikash Roy

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Bikash Roy

Online Research Specialist · SEO Strategist · Web Developer

Bikash personally verifies every calculator against official standards (WHO, NIH, government data). Online research specialist, SEO strategist, and web developer with 10+ years building accurate digital tools.

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· July 14, 2026

Why Compare the Two Methods

The Army’s official one-site method (weight + waist) replaced the legacy 3-site method (neck, waist, height, plus hip for women) in 2024, but the two don’t always agree exactly for a given person. These worked examples show both formulas side by side across a few different body types, using the same math the Army body fat calculator runs automatically.

Example 1 — Male, Average Build

Inputs: 180 lb, 34-inch waist, 15-inch neck, 5’10” (70 in) tall, age 24

One-site:

−26.97 − (0.12 × 180) + (1.99 × 34)
= −26.97 − 21.6 + 67.66 = 19.1%

Legacy 3-site:

86.010 × log₁₀(34 − 15) − 70.041 × log₁₀(70) + 36.76
= 86.010 × log₁₀(19) − 70.041 × log₁₀(70) + 36.76
≈ 86.010 × 1.2788 − 70.041 × 1.8451 + 36.76
≈ 109.99 − 129.24 + 36.76 ≈ 17.5%

Both estimates land comfortably under the 21–27 age bracket’s 22% male maximum, with the two methods differing by about 1.6 percentage points — a normal amount of spread for an average build.

Example 2 — Male, Larger Waist Relative to Frame

Inputs: 210 lb, 40-inch waist, 16-inch neck, 5’9” (69 in) tall, age 32

One-site:

−26.97 − (0.12 × 210) + (1.99 × 40)
= −26.97 − 25.2 + 79.6 = 27.4%

Legacy 3-site:

86.010 × log₁₀(40 − 16) − 70.041 × log₁₀(69) + 36.76
= 86.010 × log₁₀(24) − 70.041 × log₁₀(69) + 36.76
≈ 86.010 × 1.3802 − 70.041 × 1.8388 + 36.76
≈ 118.72 − 128.82 + 36.76 ≈ 26.7%

Both methods put this soldier above the 28–39 age bracket’s 24% maximum, meaning this profile would trigger ABCP enrollment under either formula — see the Army Body Composition Program explained for what happens next.

Example 3 — Female, Average Build

Inputs: 145 lb, 30-inch waist, 13-inch neck, 38-inch hip, 5’5” (65 in) tall, age 26

One-site:

−9.15 − (0.015 × 145) + (1.27 × 30)
= −9.15 − 2.175 + 38.1 = 26.8%

Legacy 3-site:

163.205 × log₁₀(30 + 38 − 13) − 97.684 × log₁₀(65) − 78.387
= 163.205 × log₁₀(55) − 97.684 × log₁₀(65) − 78.387
≈ 163.205 × 1.7404 − 97.684 × 1.8129 − 78.387
≈ 284.03 − 177.11 − 78.387 ≈ 28.5%

Both estimates fall under the 21–27 age bracket’s 32% female maximum, with roughly a 1.7 percentage point spread between methods — consistent with the general pattern that the two formulas rarely match exactly but usually track closely for typical body compositions.

What These Examples Show

Across all three cases, the one-site and legacy 3-site methods land within about 2 percentage points of each other — close enough to be broadly consistent, but different enough that they shouldn’t be treated as interchangeable for someone sitting right at the edge of their standard. When a result is close to the maximum for your bracket, the gap between methods is exactly the kind of margin that makes an official taping — not either self-measured formula — the only result that actually counts for ABCP purposes.

Try Your Own Numbers

Run your own measurements through the Army body fat calculator to see both methods calculated automatically and checked against your age-and-sex standard. If your self-measured result is close to the line, review common tape test measurement mistakes first — measurement error is a more common explanation for a borderline result than an actual body composition change.