I want to work out how many miles per gallon my car does, but it all feels a bit difficult cos of getting petrol in litres, and my being rubbish at any sort of conversions.Is there any sort of forumula or online calculator thingy which I could use to help me? Just did a 536 mile road trip in my 2003 Avensis 2.0 D4D. Cost of Diesel was £67.00, it took 46.56L at £1.439. What is my car's MPG? Is it ny good? Many thanks and apologies for stupid question.