Comparison of the imperial and US customary measurement systems adopted a system based on the 231-cubic-inch wine gallon for all fluid purposes. This became the US fluid gallon. Both the imperial and US fluid gallon are divided into 4 quarts, 8 pints or 32 gills. However, whereas the US gill is divided into 4 US fluid ounces, the imperial gill is divided into 5 imperial fluid ounces. So whilst the imperial gallon, quart, pint and gill are about 20% larger than their US fluid measure counterparts, the fluid ounce is about 4% smaller. Note that one avoirdupois ounce of water has an approximate volume of one imperial fluid ounce
Imperial and US customary measurement systems gallon and pint continued to be used in the retail trade for the sale of loose goods or goods measured or weighed in front of the customer. Since 1 January 2000 it has been unlawful to use imperial units for weights and measures in retail trade in the United Kingdom except as supplementary units or for the sale of draught beer and cider by the pint or milk that is sold in returnable containers. When colonies attained dominion status, they also attained the right to control their own systems of weights and measures. Many adopted the imperial system of units