Quote:
Originally Posted by everythingsablur
The only way to accurately see fuel economy is to start at a full tank, drive until you feel like refilling the tank, log that mileage, find the difference between a full tank (13.2 gallons or 50L) and how much you filled up, then calculate the fuel economy based on what you filled versus how much you traveled in that amount of fuel.
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You're complicating the math with extra nonsense. There's no reason to subtract anything from the full fuel capacity. You don't even have to know how much fuel the tank holds.
If you start with a full tank, drive 300 miles and then pump 10 gallons into the tank to fill it up again, you're getting 300/10 = 30 miles per gallon.
If you drive 250 miles and pump 10 gallons to fill it back up, you're getting 250/10 = 25 mpg.
If you drive 250 miles and pump 9.2 gallons to fill it back up, you're getting 250/9.2 = 27.17 mpg.
The calculation is exactly the same regardless of whether you use ten gallons out of a 15 gallon, 30 gallon or 100 gallon tank.