Is there a formula to figure MPG vs driving until the tank is empty then filling up? I have saved receipts for the last few times I fueled up and I wrote down the mileage on the receipt. There must be some mathmatical way to figure all this out.
The easiest and most accurate way is to total up all the gas you added from all the receipts. Then divide that into the total miles you traveled. That will give you a fairly accurate picture of your gas mileage.
“… driving until the tank is empty then filling up?”
I think you are trying to estimate how far you can drive after a fillup. Many drivers use the method of mile per tank rather than mpg. There is a formula if you know the tank’s capacity, but most drivers don’t want to empty it completely. Instead of a formula, just use the typical miles data from one fillup to the next.
You need a number of fillups, preferably from the same gas pump to get a represntative figure; one fillup will almost always be inaccurate. Mike’s suggestion will give you a fairly good figure. Never try to “top up” the tank to get it full, and never run it till empty either.
You are never really sure how much gas you used unless you use the amount on the receipt. It seems to me it’s easier to just write down the trip odometer mileage on the receipt since the last refill and then reset the trip odometer. You never need to assume haw much fuel is left, although it is easier when the low level light comes on. But you still have a couple of gallons or so in the tank, and you need to find a station quickly under those circumstances.