Cubic Inches to Imperial Gallons (in³ to gal (UK))

1 cubic inch equals 0.00360465015 imperial gallons (rounded).

1 cubic inch = 0.00360465015 imperial gallons

How to convert cubic inches to imperial gallons

To convert cubic inches to imperial gallons, multiply the number of cubic inches by 0.00360465015. The factor is rounded to 10 significant digits. To go the other way, multiply imperial gallons by 277.4194328 (rounded).

imperial gallons = cubic inches × 0.00360465015

Example: 10 cubic inches = 0.0360465015 imperial gallons.

Pints, quarts, gallons and fluid ounces differ between the US and the UK. Units are labeled 'US' or 'imperial' to avoid confusion.

About these units

Cubic Inch (in³)

US & ImperialCurrent unit

Exactly 16.387064 mL. Used for engine displacement in the US and for small mechanical parts.

Cubic inch is a unit defined by a ruler. Take an inch, build a cube, and its volume is exactly 16.387064 milliliters under the modern definition of the inch as 25.4 millimeters. Its main role in history is as the building block behind other US volumes: the US gallon is defined as 231 cubic inches, so a cubic inch is exactly 1/231 of a gallon. Even the 42-gallon oil barrel works out to precisely 9,702 of them.

The cubic inch survives most visibly in American engines, which are abbreviated c.i.d. for cubic inch displacement, while the rest of the world and many modern automakers speak in liters. A 5.7 liter engine is about 350 cubic inches, a conversion made easy by the exact factor of 16.387064. Small mechanical parts are also sized in cubic inches in North America.

1 cubic inch = 0.016387064 liters (exactly).

Sources: Wikipedia: Cubic inch; NIST SP 811, Appendix B.8: conversion factors for volume

Imperial Gallon (gal (UK))

Imperial (British)Current unit

Exactly 4.54609 liters, the volume of 10 pounds of water. Used for fuel economy in the UK (miles per gallon) and historically across the Commonwealth.

Britain unified its confusing gallons by act of Parliament in 1824. Before then, the country used separate ones for wine at 231 cubic inches, ale at 282 and corn at about 268.8. The 1824 reform replaced them with the imperial gallon, defined as the volume of ten pounds of distilled water, calculated at 277.274 cubic inches. A new definition in 1889 slightly changed that, and after the liter was restored to exactly a cubic decimeter in 1964, Canada and then the UK in 1976 adopted the exact value of 4.54609 liters.

Because the United States kept the 231-cubic-inch wine gallon, an imperial gallon is about 20 percent larger than a US gallon. That explains why a car rated at 40 miles per gallon in Britain is less impressive in American terms, since it comes to roughly 33 US miles per gallon. Ireland dropped the gallon as a primary trade unit at the end of 1993 and the UK at the end of September 1995, but it lives on in British fuel-economy figures and older recipes.

1 imperial gallon = 4.54609 liters (exactly).

Sources: Wikipedia: Gallon; UK Weights and Measures Act 1985, Schedule 1

Related conversions

See all volume units.