# Cubic inches to gallons converter

Converts cubic inches (in³) to gallons (gal) and back, with the exact unit definitions.

- Page: https://www.acalculator.org/convert/cubic-inches-to-gallons
- JSON spec: https://www.acalculator.org/convert/cubic-inches-to-gallons.json
- Version: b738ee5b9568

## Default answer

Example with the default inputs (Cubic inches (in³) 1): 1 in³ = 0.004329 gal.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| value | Cubic inches (in³) | The amount in cubic inches to convert. |
| result | Gallons (gal) | The same amount in gallons. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| value | Cubic inches (in³) | The amount in cubic inches to convert. |
| result | Gallons (gal) | The amount in gallons. |

## Method

gal = in³ × 0.004329004329 (the same as in³ ÷ 231)

## Assumptions

- 1 cubic inch = 0.004329004329 gallons, from the exact definitions in NIST SP 811.
- Cups, ounces, tablespoons, teaspoons, pints, quarts, and gallons are US customary units: 1 US cup is 8 US fluid ounces.
- Exact on the typed decimals: at most 6 decimal places (6 significant digits below 0.0001), rounded half up; an answer of 1 billion or more shows at most 15 significant digits.

## Worked examples

1. value = 1 gives result = 0.004329. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.
2. value = 231 gives result = 1. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.
3. result = 1 gives value = 231. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.

## FAQ

### How many gallons are in a cubic inch?

1 cubic inch is 0.004329 gallons, from the exact unit definitions (NIST SP 811).

### How do I convert cubic inches to gallons?

Divide by 231: gal = in³ × 0.004329004329 (the same as in³ ÷ 231). For example, 1 in³ ÷ 231 = 0.004329 gal.

### How do I convert gallons back to cubic inches?

Multiply by 231, or type the gallons into the second box and the converter works it out. 1 gallon is 231 cubic inches.

### How many cubic inches are in a gallon?

231 exactly: NIST Handbook 44 defines the US gallon as 231 in³, so gallons = in³ ÷ 231, and 1,000 in³ is 4.329004 gal. A cubic inch is 16.387064 mL exactly, (2.54 cm)³.

### Is this a US or a UK gallon?

The US liquid gallon, 231 in³ or 3.785411784 L. A UK (imperial) gallon is 4.54609 L, about 277.42 in³, so the same volume is about 17% fewer UK gallons.

## Sources

- NIST SP 811 (2008), Guide for the Use of the International System of Units, Appendix B.8: Factors for Units Listed Alphabetically (bold factors are exact), retrieved 2026-10-19. https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8
- NIST SP 811 (2008), footnote 13 to Appendix B: 1 in³ = 1.6387064 × 10⁻⁵ m³ exactly, retrieved 2026-10-19. https://www.nist.gov/pml/special-publication-811/nist-guide-si-footnotes
- NIST Handbook 44 (2026), Appendix C, General Tables of Units of Measurement: 1 US gallon = 231 cubic inches, retrieved 2026-10-19. https://www.nist.gov/document/2026-nist-handbook-44-appendix-c