Cubic inch

An engine size notated as 502 cubic inches

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 3 sides being one inch long.

The cubic inch and the cubic foot are still used as units of volume in North America, although the common SI units of volume, the liter, milliliter, and cubic meter, are continually replacing them, especially in manufacturing and high technology.

One cubic foot is equal to exactly 1728 cubic inches because 12³ = 1728.

Notation conventions

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
• cui
• 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 1728 cu in)
• roughly 1 tablespoon (1.0 US gallon = 256 US 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 9702 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.

Engine displacement

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(and the use of reciprocating engines for commercial and military airplanes and helicopters has disappeared, having been replaced by turbojet, turboprop, and gas turbine engines).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 more information and a list of cubic-inch-to-liter displacement conversions, see engine displacement.

See also

• Orders of magnitude (volume)
• Conversion of units
• Square inch
• Cubic foot