I'm trying to calculate my MPG and wanted to know when you fill up at the gas station and when it automatically stops when you have it pumping on auto does that mean it reached the 10.8 gallons or how much is that exactly? Anyone know the answer to that? Thanks

 

If you consistently use the automatic shut-off, all you need to do is divide the miles driven from your trip odometer (reset with each fill-up) by the gallons used from the gas receipt to get your miles/gal for that set of miles. It doesn't really need to be a "10.8 gal tankful". Any system is approximate, but this one works pretty well.

 

^^^

and https://www.fitfreak.net/forums/general-fit-talk/3990-gas-mileage.html