The imperial pint (568 mL) is used in the United Kingdom and Ireland and to some extent in other Commonwealth nations. There are two customary pints used in the United States: a liquid pint (473 mL) and a less-common dry pint (551 mL). This difference dates back to the British Weights and Measures Act of 1824, which standardised the various pints in use at the time to a single imperial pint throughout the British Empire. The US pints were unaffected by this and can be traced back to pre-1824 English pints. Each of these pints is defined as one eighth of the respective gallon but because of differing gallon definitions, the imperial pint is approximately 20% larger than the US liquid pint. However, whereas the imperial pint is divided into 20 imperial fluid ounces, there are 16 US fluid ounces to the US liquid pint making the imperial fluid ounce slightly smaller than the US fluid ounce.
Various Commonwealth countries, such as Canada, Australia, and New Zealand, converted to the metric system in the 1960s and 1970s; so while the term “pint” may still be in common use in these countries, it may not be the same as the imperial pint originally used throughout the Commonwealth. In the United Kingdom, the imperial system is still in use for certain purposes, and even though metric units are defined as the primary units in some specific circumstances, the pint is still defined as the primary unit for beer, cider and milk. A pint of beer served in a tavern outside of the United Kingdom and the United States may be an imperial pint, a US pint, or something different, depending on local laws and customs.
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