Cubic Inches to Gallons Converter
Convert cubic inches (in³) to gallons for engine displacement, containers, and tank volumes.
This is the legal definition of the US gallon since 1707.
Conversion Result
📐 Conversion Formulas
US Gallon (direct):
Imperial Gallon (via liters):
Key Constants:
- 1 US gallon = 231 in³ (exactly, by definition)
- 1 in³ = 0.016387064 liters (exactly)
- 1 Imperial gallon = 4.54609 liters
- Therefore: 1 Imperial gallon ≈ 277.42 in³
📝 Step-by-Step Calculation
Enter a value and convert to see the step-by-step breakdown.
Understanding Cubic Inches and Gallons
The relationship between cubic inches and gallons is fundamental in American measurement. The US gallon is legally defined as exactly 231 cubic inches, making this conversion particularly clean for US measurements.
What Is a Cubic Inch?
A cubic inch (in³) is the volume of a cube measuring 1 inch on each side. It equals about 16.387 mL or 0.5541 fluid ounces. Cubic inches are commonly used for:
- Engine displacement (e.g., a "350 cubic inch" V8 engine)
- Small container volumes
- Electronic enclosure sizing
- Pump and compressor capacities
Why 231 Cubic Inches?
The number 231 comes from the English wine gallon, defined in 1707. It was calculated as a cylinder 7 inches in diameter and 6 inches deep, which works out to 231 cubic inches (using π × 3.5² × 6 ≈ 231). This definition was carried to the American colonies and became the US gallon.
US vs Imperial Gallons
The Imperial gallon was redefined in 1824 as the volume of 10 pounds of water:
- US gallon: 231 in³ = 3.785 liters
- Imperial gallon: 277.42 in³ = 4.546 liters
- The Imperial gallon is about 20% larger
Quick Reference Table
Common cubic inches to gallons conversions:
| Cubic Inches | US Gallons | Imperial Gallons | Common Example |
|---|---|---|---|
| 57.75 | 0.25 | 0.21 | 1 US quart |
| 231 | 1 | 0.83 | 1 US gallon |
| 302 | 1.31 | 1.09 | Ford 302 engine |
| 350 | 1.52 | 1.26 | Chevy 350 engine |
| 454 | 1.97 | 1.64 | Chevy 454 big block |
| 1,155 | 5 | 4.16 | 5 gallon bucket |
| 2,310 | 10 | 8.33 | 10 gallon container |
Frequently Asked Questions
A US gallon contains exactly 231 cubic inches by legal definition. An Imperial gallon contains approximately 277.42 cubic inches.
The 231 in³ definition comes from the English wine gallon of 1707, originally the volume of a cylinder 7 inches in diameter and 6 inches deep. This equals π × 3.5² × 6 ≈ 231 cubic inches.
For US gallons, divide cubic inches by 231. For Imperial gallons, divide by 277.42. Example: 350 in³ ÷ 231 = 1.52 US gallons.
A US gallon is 231 in³, while an Imperial gallon is 277.42 in³. The Imperial gallon is about 20% larger because it was redefined in 1824 based on the weight of water.
Divide the engine's cubic inch displacement by 231. A 350 cubic inch engine has a displacement of 1.52 gallons. This represents the total volume swept by all pistons.
A 5 US gallon bucket contains 5 × 231 = 1,155 cubic inches. This equals about 18.9 liters.
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