The very best way is to ALWAYS fill the tank everytime you get gas, then
divide the distance you went, 250 miles, by the new load of fuel, 12.5
gallons. The result, 20, is your miles per gallon. Fill the tank and reset
the odometer (trip meter).

I consistantly get just a bit over 25 mpg, so in 300+ miles I put in 12
gallons of gas, for just over 325 miles, I put in 13 gallons, for 275 miles,
I get 11 gallons.

It doesn't matter how much gas is left when you fill up. It does matter if
you fill to the brim, or only fill to the first shut-off. I usually fill to
the first shut-off, then top off to the next even dollar. I used to top off
to the next even quarter, but gas is getting so expensive that topping to
the next dollar is less than a half gallon, and this won't change your
formula very much.

So, you go to the corner today and buy gas. If you filled the tank to the
top AND reset the odometer the last time you got gas, then you can divide
the distance by the new load of fuel and derive the mileage. If you did not
fill to the top and/or reset the odometer, then this tank will be your
baseline and you can make no calculations from it. Then, in a week or so
when you visit the filling station again, then you fill the tank and divide
the distance by the fuel load. The result will be your mileage. If you go
250 miles and put in 10 gallons, then you got 25 mpg. All you have to do is
always fill the tank, never just get $5.00, or whatever. If you do just get
$5.00, then you have to add the gallons to the next fill up and leave the
odometer counting as if you had not gotten the few gallons.

After you do this a few times, you will be able to quickly calculate in your
head to confirm that you are getting the same mileage that you always get. I
get 25 mpg in my normal driving routine.




"Newbie" > wrote in message
...
> It may seem like a superfluous question, but what is the best way of
> calculating what mmg yuor vehicle is getting? I have my miles reading
> of course, and I can record how much gas I put in, but there was some
> gas already there in the tank, and how do I know what was traveled on
> how much gas? If you have a good system, please share!