As we all know the world is a muddle of metric and imperial
We buy our fuel in liters, yet we are all of an age where we remember the price of a gallon
We haven`t gone completely metric yet, as we all drive in miles and not kilometers.
We all know what the phrase MPG (Miles Per Gallon) means, but with so many variables, its a nightmare to work it out.
Here`s another one of my little calculators for you to download and play with (and you can work out the fuel costs of a trip too)
www.beachbuggy.info/DNDMPGCalc.xlsx 
Open it up with Microsoft Excel and "ENABLE EDITING" - You will then be able to play around