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The cubic inch is a unit of measurement for 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 depth) being one inch long.
The cubic inch and the cubic foot are still 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 foot is equal to exactly 1728 cubic inches because 123 = 1728.
The following symbols have been used to denote the cubic inch:
- cubic in
- cu inch, cu in
- inch^3, in^3
- inch³, in³
- c.i., CI
- c.i.d., cid, CID —for cubic inch displacement in internal combustion engines
Equivalence with other units of volume
1 cubic inch (assuming an international inch) is equal to:
- 0.000578703703703 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 0.554112552 American/English fluid ounces
- about 0.069264069 American/English cups
- about 0.000465025413 American/English bushels
- about 0.004329 American liquid gallons (1.0 gallon equals 231 cu in exactly [3 in × 7 in × 11 in])
- about 0.00010307 barrels of crude oil (1.0 barrel equals 42 gallons, by definition, or 9,702 cu in)
- exactly 0.016387064 liter (1.0 liter is about 61 cu in [exactly 61.0237440947323 cu in])
- exactly 16.387064 milliliters or cubic centimeters (which in turn is approximately 0.061 cu in)
- exactly 0.000016387064 cubic meters(1.0 m³ is about 61,023.74 cu in)
Uses of the cubic inch
Electrical box volume
The cubic inch was established decades ago 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.
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. Hence the cubic inch is still used for this purpose in the context of classic car collecting and so forth. The auto industry now uses liters for this purpose (and the use of reciprocating engines for commercial and military airplanes and helicopters has disappeared, having been replaced by turbojet, turboprop, and gas turbine engines). For heritage sake, the Ford Mustang still comes in a Boss 302 version, using a five litre (302 cubic inch) engine, much like the original Boss. Chevrolet has also revived this usage on its new 427 Corvette. Dodge has a "Challenger 392" (a conversion from its 6.4 liter V8 engine).
In the UK, engine displacement is now denoted in litres. However, cubic inches were sometimes used in the past to denote model numbers. An example is the AEC Reliance bus which was available with five different engines:
- AH470, 470 cubic inches, 7.7 litres
- AH505, 505 cubic inches, 8.1 litres
- AH590, 590 cubic inches, 9.6 litres
- AH691, 691 cubic inches, 11.3 litres
- AH760, 760 cubic inches, 12.4 litres
For more information and a list of cubic-inch-to-liter displacement conversions, see engine displacement.