The UK also does for some God awful reason (especially infuriating considering it's sold by the litre at the petrol station).
In the United States and some other countries, a gallon is equal to 128 fluid ounces or 3.785 liters. Meanwhile, in the United Kingdom and some Commonwealth countries, a gallon is equal to 160 fluid ounces or 4.546 liters.
In fairness the fluid ounces are also different, an Imperial (english) fluid ounce is 28.41306mL, while a US Customary fl oz is 29.5735mL. So the Imperial floz is 96% the US customary, not enough to account for having 25% more of them in a gallon, but it does lead to the Imperial gallon only being 20% larger than the customary gallon.
But wait there’s more! The US also has the “food labelling” fluid ounce which is not the customary one, instead it’s exactly 30mL.
And yet we claim to live in a science based society.
I mean, there are a million things, that do not need universal standards, but standards are imposed anyway.
But where one standard would be really helpful, like scientific values, we have many. And some people would rather go to prison, than adopt. (I think that happened in the UK, after they force switched to metric)
The UK also uses pints for dairy milk, but litres for plant-based milks. UK must be completely disregarded if you're looking to make sense about what units to use.
In the United States and some other countries, a gallon is equal to 128 fluid ounces or 3.785 liters. Meanwhile, in the United Kingdom and some Commonwealth countries, a gallon is equal to 160 fluid ounces or 4.546 liters.