A gallon is a liquid measure, used in most English-speaking countries. Until 1826, the gallon was the same in Britain and the United States and was the standard wine measure. It measured 128 fluid ounces (16 fluid ounces to the pint and 8 pints to the gallon).
In 1826, the Imperial gallon was intro-duced into Britain which measured 160 fluid ounces to the gallon (20 fluid ounces to the pint, 8 pints to the gallon).
Today the Imperial gallon is used in Britain and the old English gallon in the United States.