Hello,
Here's a program (for Windows) called Convert, and it really can convert any unit to any other unit:
http://joshmadison.com/article/convert-for-windows/
18mpg, huh? You have some room for improvement!
That's a big car for New Zealand! When I was there (in 1982) with my family, the big cars were Volvos. My family are all over 6', so we rented a Toyota van.