This converter turns imperial gallons into cubic inches instantly, using the exact factor 1 imperial gallon = 277.4194328 cubic inches. Type any number and the result updates as you go — nothing is sent to a server, so the arithmetic happens entirely in your browser.
Exactly 4.54609 litres, about 20% larger than the US gallon. The volume of a one-inch cube, traditional for US engine displacement.
Because the relationship is a simple proportion, one multiplication does the whole job. The table further down gives pre-computed values for the amounts people look up most often, and the result panel also reports the reverse conversion so you can check the figure both ways.
The formula
imperial gallons- The amount you are converting, measured in imperial gallons
277.4194328- The exact number of cubic inches in one imperial gallon
cubic inches- The converted result
How it works, step by step
- Enter the number of imperial gallons you want to convert.
- The value is multiplied by 277.4194328, the exact conversion factor.
- The result is displayed in cubic inches, rounded for readability.
- The unrounded value and the reverse conversion appear underneath so you can verify it.
Worked examples
Converting 5 imperial gallons
Multiply 5 by 277.41943. That gives 1,387.1 cubic inches. A quick sanity check: one imperial gallon is larger than one cubic inch, so the number should get bigger — and it does.
Converting 72 imperial gallons
72 × 277.41943 = 19,974.2 cubic inches. Working backwards, 19,974.2 ÷ 277.41943 returns 72 imperial gallons, which confirms the factor is applied the right way round.
How to read your score
Frequently asked questions
How many cubic inches are in one imperial gallon?
Exactly 277.4194328. Every conversion on this page is that single number multiplied by your input, so the result carries no rounding error beyond what is shown.
What is the formula to convert imperial gallons to cubic inches?
Cubic Inches = imperial gallons × 277.4194328. To reverse it, divide instead: imperial gallons = cubic inches ÷ 277.4194328, which is the same as multiplying by 0.00360465015.
Is the imperial gallon bigger than the cubic inch?
Yes. One imperial gallon equals 277.419 cubic inches, so it is the larger unit.
Why does my answer differ slightly from other imperial-gallons to cubic-inches converters?
Most differences come from rounding the factor too early. This tool keeps full double precision through the calculation and only rounds at the final display step, and it also shows the unrounded value so you can see exactly where any difference appears.
What is a imperial gallon?
Exactly 4.54609 litres, about 20% larger than the US gallon.
What is a cubic inch?
The volume of a one-inch cube, traditional for US engine displacement.
Imperial Gallons to cubic inches reference table
| Imperial Gallons | Cubic Inches |
|---|---|
| 0.5 gal | 138.7097 in³ |
| 1 gal | 277.4194 in³ |
| 2 gal | 554.8389 in³ |
| 3 gal | 832.2583 in³ |
| 5 gal | 1,387.1 in³ |
| 10 gal | 2,774.19 in³ |
| 15 gal | 4,161.29 in³ |
| 20 gal | 5,548.39 in³ |
| 25 gal | 6,935.49 in³ |
| 50 gal | 13,870.97 in³ |
| 75 gal | 20,806.46 in³ |
| 100 gal | 27,741.94 in³ |
| 250 gal | 69,354.86 in³ |
| 500 gal | 138,709.72 in³ |
| 1000 gal | 277,419.43 in³ |
Exact factor: 1 imperial gallon = 277.4194328 cubic inches. Values rounded for display.