To work out exactly how many miles to the gallon your vehicle does:

• Every time you put fuel in the tank record the number of litres added and the number of miles on the clock (the odometer reading)


• Start a spreadsheet using Microsoft Excell, LibreOffice Calc or similar.
  Title the columns - miles, litres and miles per gallon or something like that.
  Enter the milage in the first column and the amount of fuel in the second column.
  In the third column, leave row 2 empty, in row three enter =(A3-A2)/(B2/4.5)
  As you add rows simply copy and paste cell C3 and the spreadsheet will do the rest.
  
  
  
  
• The results will vary depending on whether you fill up when half full or close to empty but they will average out over time.