How accurate is your trip meter and estimated KM left in your gas tank. Cars.com explored the trip meter vs. the notepad and gas pump. They found that there are many variables that can affect the amount of gas the pump says and how much goes into your tank, it could even be off by a half to a 10th per gallon, which could be 10% of your fill up.

The experts also discuss variables like tire size and wear affecting mileage and even the day’s  temperature. Even with so many variables the experts do agree that calculating gas mileage will average out after two or three tanks, using either method.