If you cross the pond often, it's useful to remember the following: x mpg * y l/100km = 240 (or more exactly 235 and change, but 240 has more divisors and is easier to manipulate).

Illustrated:

10 mpg = 24 l/100km

20 mpg = 12 l/100km

24 mpg = 10 l/100km

30 mpg = 8 l/100km

40 mpg = 6 l/100km

60 mph = 4 l/100km

Small cars in EU are i the 4-6 l/100km range, or between 40-60 mpg. Sedans are typically between 8-12 l/100km, or 20-30 mpg.

HTH