Cubic Inches to Gallons Converter
Enter a volume in cubic inches to get the equivalent in US gallons or UK (imperial) gallons. The result also shows fluid ounces, quarts, liters, milliliters, and cubic feet. Switch direction to convert gallons back to cubic inches. The math panel shows every step.
How to convert cubic inches to gallons
The US gallon is defined as exactly 231 cubic inches. To convert cubic inches to US gallons, divide the cubic-inch value by 231. To reverse the conversion (gallons to cubic inches), multiply the number of gallons by 231. For UK (imperial) gallons, the factor is approximately 277.42 cubic inches per gallon, so divide by 277.42 to go from cubic inches to UK gallons, or multiply by 277.42 to go the other way. Formula (US): gallons = cubic inches / 231 Formula (UK): gallons = cubic inches / 277.42 Worked example: a tank holds 462 cubic inches of liquid. Dividing by 231 gives exactly 2 US gallons, or dividing by 277.42 gives about 1.666 UK gallons.
US gallons vs UK (imperial) gallons
Despite sharing the name "gallon", the US gallon and the UK (imperial) gallon are different units. The US liquid gallon is exactly 231 cubic inches (approximately 3.785 liters). The UK imperial gallon is defined as exactly 4.54609 liters, which works out to about 277.42 cubic inches, making it roughly 20 percent larger than its US counterpart. This difference matters when reading engine displacements, fuel economy figures, or fluid container sizes imported from the UK or the US. A car advertised as getting 40 miles per gallon in the UK covers a larger volume per fill, so the raw number is not directly comparable to a US miles-per-gallon rating.
Where cubic inches appear in everyday life
Cubic inches (in³) appear most often in automotive engineering and home improvement. Engine displacement, the combined swept volume of all cylinders in an internal combustion engine, was traditionally measured in cubic inches in North America. A 350 in³ V8 engine, for example, displaces about 1.515 US gallons (or 5.735 liters) per full revolution cycle. In home improvement, the volumes of concrete pours, soil bags, planter boxes, and aquariums are sometimes given in cubic inches before converting to gallons for purchasing liquids or checking pump ratings. Knowing the cubic-inch capacity of a container makes it easy to determine how many gallons of water, paint, or fertilizer it holds.
Converting to other volume units
Cubic inches can be converted to any metric or imperial volume unit using fixed factors: - 1 in³ = 0.016387 liters (or 16.387 milliliters) - 1 in³ = 0.55411 US fluid ounces - 1 in³ = 0.017316 US quarts - 1 in³ = 1/1728 cubic feet (approximately 0.000579 ft³) - 1 in³ = 0.004329 US gallons This calculator converts all of these simultaneously so you can pick whichever unit is most useful for your application without chaining separate conversions.
Common volume equivalents in cubic inches
| Volume | Cubic inches (in³) | US gallons | Liters |
|---|---|---|---|
| 1 US fluid ounce | 1.80469 | 0.0078125 | 0.0296 |
| 1 US cup (8 fl oz) | 14.4375 | 0.0625 | 0.2366 |
| 1 US pint | 28.875 | 0.125 | 0.4732 |
| 1 US quart | 57.75 | 0.25 | 0.9464 |
| 1 US gallon | 231 | 1 | 3.7854 |
| 1 UK (imperial) gallon | 277.419 | 1.201 | 4.5461 |
| 1 liter | 61.024 | 0.2642 | 1 |
| 1 cubic foot | 1728 | 7.4805 | 28.317 |
| 5-gallon bucket | 1155 | 5 | 18.927 |
| 55-gallon drum | 12705 | 55 | 208.2 |
Standard liquid measures and their cubic inch equivalents. Use these as quick reference checkpoints.
Frequently asked questions
How many cubic inches are in a US gallon?
There are exactly 231 cubic inches in one US liquid gallon. This is a legal definition, not an approximation, established under US customary units and codified in federal law. So to convert gallons to cubic inches, multiply by 231; to convert cubic inches to gallons, divide by 231.
How many cubic inches are in a UK gallon?
One UK (imperial) gallon equals approximately 277.419 cubic inches. The imperial gallon is defined as exactly 4.54609 liters, and since 1 liter = 61.0237 cubic inches, the result is 4.54609 x 61.0237 = 277.419 in³. This makes the UK gallon about 20 percent larger than the US gallon.
What is the formula to convert cubic inches to gallons?
For US gallons: gallons = cubic inches / 231. For UK (imperial) gallons: gallons = cubic inches / 277.42. For example, 500 cubic inches / 231 = 2.1645 US gallons, or 500 / 277.42 = 1.8025 UK gallons.
How do I convert cubic inches to liters?
Multiply cubic inches by 0.016387 to get liters, or equivalently by 16.387 to get milliliters. For example, 231 cubic inches x 0.016387 = 3.785 liters (exactly one US gallon). This calculator shows the liter conversion alongside gallons so you do not need to do it separately.
Why does engine displacement use cubic inches?
Engine displacement in North America was historically measured in cubic inches because the inch was the standard unit of length in US engineering. A V8 with 350 cubic inches of displacement sweeps 350 in³ of volume per full revolution cycle across all cylinders. Modern spec sheets usually list displacement in liters, but cubic inches remain common in classic car communities, parts catalogs, and race-engine discussions.
How many cubic inches are in 5 gallons?
Five US gallons = 5 x 231 = 1155 cubic inches. Five UK gallons = 5 x 277.42 = 1387.1 cubic inches. A standard five-gallon bucket (US measure) therefore holds 1155 cubic inches of liquid at full capacity.