Cubic Inches to Gallons Converter
Convert between cubic inches and US gallons instantly. Perfect for engine displacement, aquarium volume, fuel systems, and industrial container calculations.
How many cubic inches are in a gallon?
1 US gallon equals exactly 231 cubic inches. This is a historical definition dating back to the British imperial system. The number 231 was convenient because it has many factors (3 × 7 × 11), making it easy to divide for various sub-units. To visualize: a gallon is 231 in³, which means a box measuring 11 inches × 7 inches × 3 inches = 231 in³ = exactly 1 gallon. This conversion is essential for engine displacement, fuel systems, and aquarium volume calculations.
How do I convert cubic inches to gallons?
To convert cubic inches to gallons, divide by 231. Formula: Gallons = in³ ÷ 231. Examples: 231 in³ = 1 gal, 500 in³ = 2.164 gal, 1,000 in³ = 4.329 gal, 5,000 in³ = 21.645 gal. For reverse (gallons to cubic inches), multiply by 231: 5 gal = 1,155 in³, 10 gal = 2,310 in³. Engine displacement example: a 350 CID (cubic inch displacement) engine = 350 ÷ 231 = 1.515 gallons of total cylinder volume. Aquarium example: a 55 gal tank = 55 × 231 = 12,705 in³.
Why are engine sizes measured in cubic inches or liters?
Engine displacement is the total volume swept by all pistons in an engine. US engines historically used cubic inches (CID), while the rest of the world used liters (L) or cubic centimeters (cc). Conversion: 1 L = 61.0237 in³. Classic engine sizes: 350 CID = 5.7 L (Chevy small-block V8), 302 CID = 4.95 L (Ford 5.0), 427 CID = 7.0 L (big-block V8), 454 CID = 7.44 L (Chevy big-block). Modern engines use liters: a 2.0 L = 122 in³, a 3.6 L = 220 in³. This converter helps compare engine sizes across systems.
How do I calculate aquarium volume in gallons?
To find aquarium volume in gallons: 1. Measure length, width, and height in inches. 2. Multiply: Volume (in³) = L × W × H. 3. Divide by 231: Gallons = in³ ÷ 231. Example: a 48" × 13" × 21" tank = 13,104 in³ ÷ 231 = 56.7 gallons (standard 55-gallon tank). For a bow-front tank, multiply by 0.85 for the curved front. Always subtract 10-15% for displacement from gravel, decorations, and equipment. This calculator does the in³ to gallons step instantly.