Cubic Inches to Gallons Converter
Convert cubic inches to gallons for engines, tanks, and containers. Enter cubic inches and choose US or imperial gallons; results include liters and cubic feet. A US gallon is exactly 231 cubic inches.
Example: with Cubic inches 231 · Gallon type US gallon (231 cu in) → Gallons: 1 US gal.
- In liters3.7854 L
- In cubic feet0.13368 cu ft
Computed by the calculator below using its default values. Change any input to see your own numbers.
A US gallon is defined as exactly 231 cubic inches, so US gallons = cubic inches ÷ 231.
231 cubic inches to the gallon
The US gallon is not an arbitrary metric conversion — it is defined as exactly 231 cubic inches. So converting cubic inches to US gallons is a clean divide by 231. That is why engine displacement and container sizes translate so neatly: 462 cubic inches is exactly 2 gallons, 231 is exactly one.
In liters, a cubic inch is 16.387064 milliliters, so 231 cubic inches works out to the standard 3.785 liters of a US gallon.
US versus imperial
The imperial (UK) gallon is not tied to 231 cubic inches. It is 4.54609 liters, about 277.4 cubic inches, so the same cubic-inch volume gives fewer imperial gallons. Choose the gallon type that matches your spec before reading the result.
Cubic inches show up on US engine specs and older tanks; the liters figure is the safest common ground when a document is unclear about which gallon it means.
How it’s calculated
US gallons = cubic inches ÷ 231 (a US gallon is defined as 231 cubic inches exactly). Liters = cubic inches × 16.387064 ÷ 1000. Imperial gallons = liters ÷ 4.54609. Cubic feet = cubic inches ÷ 1728.
Assumes the container is filled to the stated volume; real tanks lose capacity to walls and fittings.
Cubic inches to US gallons and liters
| Cubic inches | US gallons | Liters |
|---|---|---|
| 100 | 0.4329 | 1.6387 |
| 231 | 1.0000 | 3.7854 |
| 500 | 2.1645 | 8.1935 |
| 1,000 | 4.3290 | 16.3871 |
| 1,728 | 7.4805 | 28.3168 |
1 US gallon = 231 cubic inches exactly; 1 cubic inch = 16.387064 mL (NIST).
Common mistakes
- Dividing by the wrong figure — it is 231 cubic inches per US gallon, not 128 or 1,728.
- Applying the 231 rule to imperial gallons, which are about 277.4 cubic inches.
- Confusing cubic inches of volume with square inches of area.
- Assuming a full tank equals its box volume; walls and fittings reduce it.
Frequently asked questions
How many cubic inches are in a gallon?
A US gallon is exactly 231 cubic inches. So to convert cubic inches to US gallons, divide by 231.
What is the formula for cubic inches to gallons?
US gallons = cubic inches ÷ 231. For liters, multiply cubic inches by 16.387064 and divide by 1,000.
How many gallons is a 350 cubic inch engine?
About 5.73 liters, or 1.52 US gallons of displacement. Divide 350 by 231 to get the gallon figure, though engines are usually quoted in liters.
Does 231 work for imperial gallons?
No. The 231 cubic inch definition is only for the US gallon. An imperial gallon is 4.54609 liters, about 277.4 cubic inches.