Cubic inch
An engine with a swept piston displacement of 502 cubic inches
General information
Unit system	Nonstandard
Unit of	volume
Symbol	in3, cu in
Conversions
1 in3 in ...	... is equal to ...
SI derived units	≈ 16.387 mL
US customary	1⁄231 US Gallon
nonstandard	1⁄1728 ft3

The cubic inch (symbol in³) is a unit of volume in the Imperial units and United States customary units systems. It is the volume of a cube with each of its three dimensions (length, width, and height) being one inch long which is equivalent to 1/231 of a US gallon.^[1]

The cubic inch and the cubic foot are used as units of volume in the United States, although the common SI units of volume, the liter, milliliter, and cubic meter, are also used, especially in manufacturing and high technology. One cubic inch is approximately 16.387 mL.

One cubic foot is equal to exactly 1,728 cubic inches (28.32 L) because 12³ = 1,728.^{[citation needed]}

Notation conventions

• The following abbreviations have been used to denote the cubic inch: cubic in, cu inch, cu in, cui, cu. in.
• The IEEE standard symbol is: in^3[1]
• In internal combustion engines, the following abbreviations are used to denote cubic inch displacement: c.i.d., cid, CID, c.i., ci

Equivalence with other units of volume

One cubic inch (assuming an international inch) is equal to:

• 0.000578704 cubic feet (1 cu ft equals 1,728 cu in)
• Roughly 1 tablespoon (1.0 U.S. gallon = 256 U.S. tablespoons = 231 cubic inches)
• About 0.576744 imperial fluid ounces
• About 0.554113 US fluid ounces
• About 0.06926407 American/English cups
• About 0.000450581 imperial bushels
• About 0.000465025 US bushels
• About 0.00360465 imperial gallons
• About 0.00432900 US gallons (1.0 gallon equals 231 cu in exactly [3 in × 7 in × 11 in])
• About 0.0001030715 barrels of crude oil (1.0 barrel equals 42 gallons, by definition, or 9,702 cu in)
• Exactly 0.016387064 liters (1.0 liter is about 61.0237 cubic inches)
• Exactly 16.387064 milliliters or cubic centimeters (which in turn is approximately 0.0610237 cubic inches)
• Exactly 1.6387064×10⁻⁵ cubic meters (1.0 m³ is about 61,023.7 cubic inches)

Uses of the cubic inch

Electrical box volume

The cubic inch was established decades ago in the National Electrical Code as the conventional unit in North America for measuring the volume of electrical boxes. Because of the extensive export of electrical equipment to other countries, some usage of the non-SI unit can be found outside North America.

Engine displacement

North America

The cubic inch was formerly used by the automotive industry and aircraft industry in North America (through the early 1980s) to express the nominal engine displacement for the engines of new automobiles, trucks, aircraft, etc. The cubic inch is still used for this purpose in classic car collecting. The auto industry now uses liters for this purpose, while reciprocating engines used in commercial aircraft often have model numbers based on the cubic inch displacement. The fifth generation Ford Mustang has a Boss 302 version that reflects this heritage - with a five-liter (302 cubic inch) engine similar to the original Boss. Chevrolet has also revived this usage on its 427 Corvette. Dodge has a "Challenger 392" (a conversion from its 6.4 liter V8 engine).