Cubic inch

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.

Cubic inch
An engine with a swept piston displacement of 502 cubic inches
General information
Unit system	Nonstandard
Unit of	volume
Symbol	in^3, cu in
Conversions
1 in^3 in ...	... is equal to ...
SI derived units	16.387064 mL
US customary	⁠1/231⁠ US gallon
nonstandard	⁠1/1728⁠ ft^3

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 exactly 16.387064 mL.

One cubic foot is equal to exactly 1,728 cubic inches (28.316846592 L), as 12³ = 1728.

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: in³
• 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 is equal to:

• Exactly ⁠1/1728⁠ cubic feet
• Exactly ⁠1/231⁠ US gallon
• Exactly ⁠4/231⁠ US liquid quart
• Exactly ⁠8/231⁠ US liquid pint
• Exactly ⁠32/231⁠ US gill
• Exactly ⁠128/231⁠ US fluid ounce
• Exactly ⁠1+25/231⁠ US tablespoons
• Exactly ⁠3+25/77⁠ US teaspoons
• Exactly ⁠4+100/231⁠ US fluid drams
• Exactly ⁠50/107521⁠ US bushel
• Exactly ⁠1600/107521⁠ US dry quart
• Exactly ⁠3200/107521⁠ US dry pint
• ≈0.00360465 imperial gallons
• ≈0.0144186 imperial quarts
• ≈0.0288372 imperial pints
• ≈0.1153488 imperial gills
• ≈0.576744 imperial fluid ounces
• ≈1.153488 imperial tablespoons
• ≈4.613952 imperial fluid drams
• ≈0.00045058 imperial bushels
• Exactly ⁠1/9702⁠ barrel of crude oil
• Exactly 16.387064 milliliters

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).

See also

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