The cubic inch is a unit of volume derived from the imperial unit system and uses the symbol in³.
1 cubic inch is defined as equal to the volume of a cube with edges measuring 1 in. It is equivalent in volume to 16.387 ml, 1/231 US gallons and 1/1728 ft³.
Common uses for cubic inches include quantifying the size of electrical boxes and in the automotive industry for measuring engine displacement. The 5th generation Ford Mustang ran on a Boss 302 which was a 302 in³ engine (5.0L).
The cup is a unit of volume in the US customary unit system with the symbol cup.
It is equal to 1/2 US customary pint, 1/4 US customary quart and 1/16 US customary gallon. it is also equal to 236.5882365 millilitres.
Used primarily for cooking - the cup was adopted and established as a recognised unit of measure as it could be used by almost anyone in any kitchen. Due to the slight variants in design and size, it is rarely used as an accurate measure for important or critical materials, however it does represent a specific amount and can be used across many recipes to indicate what is needed.