Knowing how many miles your car is getting for each gallon of fuel it burns measures how efficiently your car is running. Sudden drops in fuel economy can indicate a potential problem with the vehicle. Once you have an estimate of how many miles your car gets per gallon, you can estimate how far you have driven based on how much gas your car has used. However, since driving conditions are always different, this will only be an estimate rather than an exact figure.
Fill your gas tank until it is full and note the odometer reading.
Drive until you need to refill your gas tank.
Fill the car again with gas, noting how many gallons it took to refill the car and the odometer reading.
Note the difference between the starting odometer reading and the ending odometer reading to determine how many miles you have driven. For example, if the odometer started at 76,500 and ended at 76,860, the difference would be 360 miles.
Divide the number of miles driven by the number of gallons of gas used. For example, if you used 15 gallons to drive 360 miles, you would be getting 24 miles per gallon.
