The US dry gallon is a unit of volume in the US customary unit system with the symbol dry gal.
The dry gallon is equal to 268.8025 in³ or 4.404 L.
The US dry gallon is not used anywhere any more - the unit below is the dry pint and the unit above is the bushel.
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.