What is the Cubic Inch ?

Source: en.wikipedia.org

" 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 depth) being one inch long which is equivalent to 1/231 of a US gallon.
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. "