Convert Cubic Inches to US Gallons

Formula

gal (US) = in³ ÷ 231

Derivation from SI units:

• 1 in³ = (0.0254 m)³ = 1.6387064 × 10⁻⁵ m³ = 16.387064 cm³
• 1 US gal = 231 in³ = 231 × (0.0254 m)³ = 0.003785411784 m³
• 1 in³ = 0.000016387064 m³ ÷ 0.003785411784 m³ per gal (US) = 0.004329004329004 gal (US)

Both units are defined exactly, so the factor is exact. Cubic Inch definition: cubic inch; US Gallon definition: US gallon.

Worked examples

1. A reading of 61.024 in³ converts to 0.2641731602 gal (US).
   61.024 in³ × 0.004329004329 = 0.2641731602 gal (US)
2. A value of 350 in³ is 1.515151515 gal (US).
   350 in³ × 0.004329004329 = 1.515151515 gal (US)

Where it's used

Cubic Inches are used for US engine displacement (e.g. 350 cubic inches ≈ 5.7 L), while US gallons appear in fuel, water and chemical volumes in the US. Both measure volume (capacity), so the conversion is a fixed factor.

Cubic Inch to other volume units

Frequently asked questions

Sources

• Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "cubic inch (in³)".
• Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "gallon [U.S.] (gal)".
• NIST Handbook 44, Appendix C: General Tables of Units of Measurement, National Institute of Standards and Technology , Appendix C.

Last reviewed: 2026-10-15. Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.