Bear in mind that the gallon we use is different from the US gallon, too:
a UK gallon is eight (imperial) pints of 20 fluid ounces, so 4.54 litres
a US gallon is 231 cubic inches, so 3.79 litres
The reason that I thought American car fuel economy was so terrible as a child is partly because UK mpg is +20% on US mpg for the same car on the same fuel. But also, because American car fuel economy is so terrible.
Bear in mind that the gallon we use is different from the US gallon, too:
The reason that I thought American car fuel economy was so terrible as a child is partly because UK mpg is +20% on US mpg for the same car on the same fuel. But also, because American car fuel economy is so terrible.
Don’t forget that the UK fluid ounces are different (slightly smaller) than the US fluid ounces as well
20 UK fl oz = 19.21 US fl oz