Cubic Inches to Gallons Converter

The U.S. gallon is defined as exactly 231 cubic inches. Engine displacements, tank sizes and container capacities in cubic inches convert directly.

How to use the Cubic Inches to Gallons Converter

1. Type the number of cubic inches into the Cubic inches field. Decimals such as 115.5 are fine.
2. Read the answer in US gallons – it updates as you type, with no button to press.
3. To convert the other way, type into US gallons and the cubic inches are recalculated.
4. Press Copy results to copy both values with the page title, or Copy link to share this exact conversion.

This page converts only in³ ⇄ US gal. Need a different unit? Use the general volume converter, where you can choose any “from” and “to” unit.

How it works

Both units measure volume, so they are always in the same ratio: one cubic inch equals 0.0043290043 US gallons. The calculator multiplies the number of cubic inches you type by 0.0043290043 to give US gallons, and when you type into the US gallons field it divides by the same factor to give cubic inches. Because the ratio never changes, doubling the cubic inches always doubles the US gallons. Results are calculated at full precision and rounded only for display (up to eight decimal places, with very large or small values shown in scientific notation).

How to convert cubic inches to US gallons

1. Write down the value in cubic inches, for example 231 in³.
2. Multiply by the conversion factor 0.0043290043 (because 1 cubic inch = 0.0043290043 US gal).
3. 231 × 0.0043290043 = 1 US gal.
4. To go back from US gallons to cubic inches, divide by 0.0043290043 – or multiply by 231.

in³ to US gal conversion table

What is a cubic inch?

A cubic inch is about 16.39 mL. The U.S. gallon is defined as exactly 231 cubic inches, and classic American engine sizes are given in cubic inches (e.g. 350 ci).

What is a US gallon?

The U.S. liquid gallon is exactly 231 cubic inches, about 3.785 litres. It is used for fuel, milk, water and paint in the United States.

Quick mental conversion

For a fast estimate, multiply cubic inches by about 0.0043 to get US gallons; the error is about 0.7%. Use the calculator above when you need the exact figure.

Common mistakes to avoid

Mixing u.s. and uk gallons, pints and fluid ounces, assuming a cup is always 250 ml, and treating volume and weight as interchangeable for anything except water.