How Fuel Efficient is Your Vehicle?

With gasoline prices creeping ever higher each day, many consumers are, once again, thinking about the fuel efficiency of their own vehicles. Some may already have a rough idea of their vehicle’s miles per gallon performance and some may already own a vehicle that shows the overall MPG on a computerized display. What can an individual do if he/she does not know the fuel efficiency or wants to confirm the accuracy of the computerized read- out? Is there a way to measure miles per gallon?

Calculating MPG:

Fortunately, there is a simple way to calculate your vehicles miles per gallon fuel efficiency. It requires recording a few numbers and then performing some simple math. Here is what you need to do:

Fill your tank with gasoline. For consistency and to ensure the most accurate calculations possible, run the pump at the gas station until it hits the auto shut- off. Do not try to pump any more gasoline. Stop when it hits the auto- shut-off.
Make a note of your odometer reading immediately after filling the tank, before you leave the gas station. Write down the miles and keep the number in a safe place. If you have a resettable trip counter, use it instead, but make sure that no one resets the trip counter again until the completion of your MPG measurement.
Drive your vehicle like normal and continue driving until it is close to running out of fuel. There is no steadfast rule to follow here, but it is best to wait until the fuel gage is below one- quarter tank before moving to the next step. The further you drive, the more accurate your MPG measurement.
Once the tank has slipped below the one- quarter mark, go back to the gas station and fill up again. Like before, stop pumping as soon as the auto- shut- off confirms your tank is full. Look at the fuel pump and make a note of the total gasoline purchased. The number of gallons you see, on the pump, represents the exact amount of fuel that was needed to refuel your tank since the last fill- up.
Next, get back into your vehicle and check the odometer. If you have been using the trip counter, check the miles driven and write it down. If you have been using your odometer, take the new mileage number and subtract the previous odometer reading from step #2 above. This represents the total miles driven.
Finally, take the miles driven from step #5 and divide it by the gallons of fuel purchased from step #4. This calculation represents your vehicle’s miles per gallon.

Let’s run through an example:

I fill up my fuel tank and note the odometer reading of 45,302 miles.
I go back several days later when my tank is almost empty and fill it up again, noting that it took 16.5 gallons.
I now check the odometer and it reads 45,668. Subtracting the previous reading of 45,302 means I drove my car 366 miles and I used 16.5 gallons of gas in the process.
Finally, I access the calculator on my cell phone and divide 366 by 16.5. The calculator responds with 22.18, which represents my miles per gallon.

As you can see, calculating MPG is not a difficult process. It involves simple math and it is a good idea to make this calculation even if your vehicle already provides a computerized MPG calculation. The reason is because the methodology described above is very precise. You are checking the exact miles driven and comparing it to the exact amount of fuel used to drive that number of miles. This is the most precise way to confirm the miles per gallon of any vehicle.

Here at Money Saving Parent headquarters, we have a computerized readout of MPG on our Honda hybrid but I have still checked the MPG using the steps above and have found out that the computerized MPG is slightly higher than reality. Last time I performed this exercise, my Honda computer showed 46.7 miles per gallon, but the true calculation showed 45.1. Thus, the computer estimation is reasonably close, but it was still a little off and it shows that these computerized systems in modern- day vehicles are not as accurate as many believe.

Many factors can affect miles per gallon. If you spent a good deal of time sitting idle in gridlock traffic, then there is a good chance your MPG will be lower than usual. Likewise, if your previous days of travel including cruising down the highway for long periods of time, your MPG will be higher than usual. This is why it is a good idea to run through the above steps periodically to see if your miles per gallon fluctuate widely. Even certain types of routine maintenance or vehicle improvements (oil change, air filter change, new tires, etc.) can have an impact on MPG, so it is a good idea to check your vehicle’s fuel efficiency on a regular basis.

Gasoline prices continue to edge higher and consumers need to do what they can to keep these costs under control. Finding your vehicle’s miles per gallon is a good first step. It takes only a small effort, but the information it provides can prove invaluable as you work through your family budget and look for ways to control rising gasoline costs.