How do you accurately determine what your car's actual mpg usage is?

Answer 1

The answers above provide a method for getting a reasonable single-tank estimate. The variation in fill level from fill-up to fill-up can still add significant uncertainty, however, and you will also see effects from weather and driving cycle variations.

To get a more accurate picture of what your fuel economy is over time, write down how much fuel you add and the odometer reading every time you add fuel. You can then use a program like excel to calculate the moving average of fuel economy over several tankfuls (I suggest 3 or 4 tankfulls), which significantly reduces variation due to fill level. If you keep doing this for a long time, you'll start to notice seasonal variations in fuel economy too.

Answer 2

1) Top off the fuel tank
2) write the mileage down that is displayed on your odometer
3) Drive the vehicle until you get below your last quarter of the tank of gas. Don't run the vehicle out of gas.
4) Fill the tank up again
5) Write down how many gallons it took to fill the tank up
6) Divide the miles you drove by the gallons of gas it took to fill the tank.
7) Answer: = miles per a gallon

Answer 3

If you have a trip odometer, reset it every time you refuel.

When ever you fill up, take the miles you have driven since the last time you fueled up and divide it by the amount of gallons you put into your vehicle. Don't top it off, as it will screw up the figures, always run it until it stops automatically.

Ex.

I drove 410.1 miles and put in 16.82 gallons into my truck.

410.1 / 16.82 = 24.38 mpg (rounded to the nearest hundredth).

Answer 4

Fill up your gas tank and record mileage

Drive until your gas tank is almost empty and record mileage

Log amount of gas to completely fill your tank

Divide amount of gas into miles driven = gas mileage