The imperial gill is further divided into five fluid ounces whereas the US gill is divided into four fluid ounces, meaning an imperial fluid ounce is of an imperial pint, or of an imperial gallon, while a US fluid ounce is of a US pint, or of a US gallon. Since the imperial gallon, quart, pint, cup and gill are approximately 20% larger than their US counterparts, these are not interchangeable, while the imperial fluid ounce is only approximately 4% smaller than the US fluid ounce, and they are often therefore used interchangeably.