Someone on Mastodon pointed out a useful thing today:
One mile per gallon is exactly the same thing as one furlong per pint.
So if anyone quotes their fuel consumption in furlongs-per-pint, you’ll now know what it means. Pleasingly, this works even in America.
Once you’ve impressed your friends at the pub with that one, you can point out that one mile per gallon is about 3 leagues per firkin.