Question about calculating MPG

[Emerge]

In the sticky at the top of the forum it says to divide your trip miles by the number of gallons it takes to fill up the tank again. But, logically, doesn't it make more sense to divide the trip miles by the amount of fuel you put in the first place?

If I were to be using the method I just described, would it make a big difference?

[YarisOwnersDad]

Fill the tank and set trip odometer to zero. Drive until you need gas again. Fill the tank again, and the amount of gas it takes to fill it the second time is the gas that you ran out while accumulating the miles indicated on the trip odometer. Divide that number of miles by the number of gallons it took to fill the tank the second time. Set the trip odometer back to zero again and repeat for the next MPG check.

You ALWAYS have to start with a full tank to check MPG. When you fill the tank the next time, that is how much gas you have used to drive whatever number of miles you have driven.

Tom

[BailOut]

Over time you would end up with the same average so it wouldn't matter, but it's more logical to calculate when you have both variables at once (tank miles plus tank fill amount).

Your method would require tracking what you consumed on your last fill up for as long as the tank lasts, which for me is about 2 weeks in the summer. That's a lot of work to get the same result.

[b_hickman11]

Originally Posted by Emerge

In the sticky at the top of the forum it says to divide your trip miles by the number of gallons it takes to fill up the tank again. But, logically, doesn't it make more sense to divide the trip miles by the amount of fuel you put in the first place?

If I were to be using the method I just described, would it make a big difference?

NO. Lets say your first fillup was 10 gallons and then you traveled 80 miles and filled up again. You wouldnt divide 80 by 10. You wouldnt divide 80 by how much you put in the second time which would probably only be about a gallon or so.

[127.0.0.1]

Originally Posted by YarisOwnersDad

Fill the tank and set trip odometer to zero. Drive until you need gas again. Fill the tank again, and the amount of gas it takes to fill it the second time is the gas that you ran out while accumulating the miles indicated on the trip odometer. Divide that number of miles by the number of gallons it took to fill the tank the second time. Set the trip odometer back to zero again and repeat for the next MPG check.

You ALWAYS have to start with a full tank to check MPG. When you fill the tank the next time, that is how much gas you have used to drive whatever number of miles you have driven.

Tom

and....for the most accurate measurement, [without using your own graduated cylinder]

try to do this 3 times in a row, using the same gas station, same pump, parked in the exact same spot, and same time of day (early morning is best)
for the most accurate mpg calculations.

different pump handles shut off tolerance can vary by 1-5 tenths

[MadMax]

For a truly accurate fuel mileage, you need to average your results out over as long of a period of time as possible.

There are far too many independent variables to honestly know how well your car is doing with just one tank...

Many, as you can see, use GasSavers.org to track their results.

[Emerge]

I guess I've been doing it wrong. But, the good thing is that I've been keeping track in a little notebook, so all I have to do is reconfigure my equation.

Thanks fellas.

[Emerge]

The method you guys described actually boosted my MPG numbers. :)

[why?]

i think the most accurate way would be to get a scanguage.

and congrats on higher numbers. now what are they?

[Emerge]

I'm considering a scanguage. The numbers were slightly higher now that I calculated the MPG correctly. My mean is in my sig.

[Yaris Hilton]

A Scangauge is a good thing to have for showing instantaneous and trip mileage, which can help you to adjust your driving technique to improve your mileage. But what it's showing is actually an estimate, which you have to cross check against the real mileage figure you get from dividing the miles driven by the fuel you put in when you gas up. It'll probably be very close when you get the device programmed right, but not exact.

[CKaelin]

Scanguage is Great!

[smell my finger]

I use the Road Trip app on the iPhone to track my milage. There is a free version which is great but I ended up buying it cuz with the paid version you can export your data. Milage is just something fun for me to obsese over.

[why?]

Originally Posted by Yaris Hilton

A Scangauge is a good thing to have for showing instantaneous and trip mileage, which can help you to adjust your driving technique to improve your mileage. But what it's showing is actually an estimate, which you have to cross check against the real mileage figure you get from dividing the miles driven by the fuel you put in when you gas up. It'll probably be very close when you get the device programmed right, but not exact.

i think that is the best way to use a scanguage, to see an instant average, so you can make it higher. even if it is off a bit, the main point is you now have a goal to beat.

[Yaris Hilton]

Right.