@paco @ShadowJonathan in both the gallon is the base unit but british imperial defines the gallon as the volume of 10lbs of water (nowadays defined precisely in liters) and equal to 160 fl oz, while us customary defines the gallon as 231in³ and equal to 128 fl oz (thus while imperial fl oz are smaller than us fl oz, imperial pints/quarts/gallons are larger than in the us)