Cubic Inches to Gallons
Source: NIST SP 811 Appendix B.9 and NIST Handbook 44 Appendix C for the US liquid gallon, and the Weights and Measures Act 1985 Schedule 1 for the Imperial gallon · Source verified August 14, 2026
A volume conversion tool that turns cubic inches into gallons. The US liquid gallon is defined as exactly 231 cubic inches, so this conversion is the gallon’s own definition rather than a derived factor. The Imperial gallon works out to about 277.419 cubic inches.
Start with a figure in cubic inches and read it back in gallons. Pick the US liquid or Imperial gallon, and the formula, the working, and the reference table all follow your choice.
Quick Answer
Divide cubic inches by 231 for US liquid gallons. For example, 500 cubic inches is 2.16 US gallons.
Gallon standard
1 US liquid gallon = 3.785411784 liters. The Imperial gallon is about 20% larger than the US one, so switching changes every figure below.
Answer in US liquid gallons
1 gal
231 in³ × 0.004329 = 1 gal
231 cubic inches is 1 US liquid gallon.
The unit relationships are exact by definition. The calculator derives this factor from those definitions, runs the calculation in double-precision floating point, and rounds the displayed result to six significant digits.
Entered: 231 in³
Examples
100 in³
= 0.4329 US gal
231 in³
= 1.0000 US gal
500 in³
= 2.1645 US gal
1,000 in³
= 4.3290 US gal
How it works
Formula · US liquid: gal = in³ ÷ 231 · Imperial: gal = in³ ÷ 277.41943 approximately
This is the conversion the US gallon is built from. The US liquid gallon is defined as exactly 231 cubic inches, so dividing by 231 is not an approximation but the definition itself.
US liquid gallon
gal = in³ ÷ 231
Imperial (UK) gallon
gal = in³ ÷ 277.41943 (approx)
Both factors come from definitions rather than measurement. The US liquid gallon is 231 cubic inches and the Imperial gallon is 4.54609 liters, both fixed by the standards cited below. Shorter decimals you may see elsewhere are these same values rounded.
Which gallon do you mean?
“Gallon” is not one unit. The two in common use differ by about 20%, which is far too much to ignore:
- US liquid gallon, 3.785411784 liters. The default here, and what United States fuel, beverage, and recipe figures mean.
- Imperial gallon, 4.54609 liters. About 20% larger. Used in the United Kingdom and parts of the Commonwealth.
There is also a US dry gallon, a separate unit for dry goods that this page does not convert. If a figure came from a fuel pump, a drinks label, or a recipe, it is a liquid gallon.
Cubic Inches to Gallons reference table
Converted columns are rounded for display, so they are equivalents rather than exact statements. Both gallon standards are shown side by side.
| Cubic Inches | US liquid gal | Imperial gal | Note |
|---|---|---|---|
| 100 in³ | 0.43290 | 0.36047 | |
| 231 in³ | 1.00000 | 0.83267 | One US liquid gallon, by definition |
| 500 in³ | 2.16450 | 1.80233 | |
| 1,000 in³ | 4.32900 | 3.60465 | |
| 1,728 in³ | 7.48052 | 6.22884 | One cubic foot |
| 5,000 in³ | 21.64502 | 18.02325 |
Common mistakes
- Applying 231 to the Imperial gallon. 231 cubic inches defines the US liquid gallon only. An Imperial gallon is about 277.42 cubic inches.
- Confusing cubic inches with fluid ounces. A US fluid ounce is 1.8046875 cubic inches, not one.
- Using a linear inch factor on a volume. Cubic units cube the linear relationship, so the numbers are much larger than intuition suggests.
Sources
- NIST Special Publication 811, Appendix B.9, which gives the inch as exactly 2.54 cm. Cubing that gives the cubic inch as exactly 16.387064 cm³.
- NIST Handbook 44, Appendix C, which defines the US liquid gallon as 231 cubic inches. With the inch above that fixes the US gallon at exactly 3.785411784 liters.
- Weights and Measures Act 1985, Schedule 1, which defines the Imperial gallon as 4.54609 cubic decimetres, that is 4.54609 liters.
These relationships are exact as definitions. The calculator derives its factor from them, computes in double-precision floating point, and rounds what it displays.
Related converters
- Cubic feet to gallons for larger volumes measured in feet.
- Gallons to liters to take the gallon answer into metric.
- Volume calculator to work out the cubic inches of a shape first.
- Volume converter for cups, pints, quarts, and more.
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