Definitions The gallon currently has one definition in the imperial system, and two definitions (liquid and dry) in the US customary system. Historically, there were many definitions and redefinitions.
DeFinitioNs tHE gAllon currEntLY hAs oNe dEfiNitIon In the iMperial sYsTem, and tWo deFinitIonS (lIQuid And dry) in THe Us customary SYSTem. HIstoRICally, there wErE maNY DefinitIons aNd REdefiNItIons.