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.
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.
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)
1 ft = exactly 30.48 cm; One pound is exactly 0.45359237 kilograms as in 0.453592370000000000… kilograms.