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
Pint pint can still be the principal unit used, otherwise metric units (usually the non-SI litre) must be used. There is no requirement for the litre quantity to be round numbers: thus the quantity of milk sold in a non-returnable container may be 1 pint, but will have "568 ml 1 pint", or just "568 ml" on the label. Many recipes published in the UK and Ireland still give ingredient quantities in imperial, where the pint is often used as a unit for larger liquid quantities. The Guild of Food Writers recommends that new recipes be published in metric units. The