There's a great Simpsons joke where Grandpa says, "the metric system is the tool of the devil, my car gets 40 rods to the hog's head, and that's the way I like it!"
Thus, 40 rods to the hog's head is 7.875 miles per gallon, 29.87 L/100km, or 3.348 km/L.
EDIT: sorry, 1 hogshead is 63 US gallons. This comes to about 0.002 miles per gallon... yikes! (divide all the numbers in the previous paragraph by 63^2)
Wait. I’m seeing that hogshead is like 63 “wine” gallons, not 1/63 gallon. (Not sure conversion of wine gallons to usual gallons though.)
I think my brain was subconsciously seeking a miles-per-gallon result in a "reasonable" order of magnitude. Edited original comment.
The Canadian metric equivalent is the metric crap tonne.
https://www.theregister.com/Design/page/reg-standards-conver...