How do YOU calculate your M.P.G.?

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Mike Wilson

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Should be a simple question, but I see so many on here complain about their gas mileage.

I'm wondering if there is not a discrepancy in the way some members calculate their

M.P.G.s? I know driving habits play a big role, as well as trailer towing, etc...

My fill up today, for example: (@ 2.79.9/Gallon, Lewis Co., TN.), $52.00:



425 miles, divided by 18.7 gallons to fill, = 22.7 miles per gallon.



Am I doing something wrong on the math?:unsure:
 
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Tiger, $10 to go 120 miles, with my math (@ 2.79.9, Lewis Co., TN. price )

is about 33 M.P.G. What are you driving? Again, that is figuring our local price of

2.79.9 per gallon. This might be where some of us go wrong. What is your

price per gallon?
 
tracnblack,



Your way is the way I calculate my mileage. I drive like a maniac, so I only average 16 to 18 MPG locally. On long trips, if I watch my speed, I can get 21 MPG. The area I live in has many hills and I like to fly up those hills, burning more gas.



Honestly, i think the gas prices are more in people heads then it hurts their wallet. $60.00/week in fuel is cheap compared to the price people pay in other parts in the world. I average 320 to 350 miles a week. I choose not to have a job that requires me to drive 30+ miles one way. 10 miles each way, about 15 to 20 minutes of driving, works great for me. Enough time to spend with myself, but far enough away that I don't have to look at the place on my days off.



I have a feeling that many people drive until it hits 3/8 of a tank then fill up and only see 250 miles per tank. I drive mine till it is on E, then I drive two more days.





Tom
 
I usually write down my miles before I fill up at the tank (say 85,994) fill up (roughly 22 gallons or what have you) than write down what my miles are when I go to fill up again. Fill it up and see how many gallons I put in Vs 22 gallons. If that makes sense...its 3am.



85,994 start.

86,294 end.



300 miles on 22 gallons of gas and I only filled up with 15 gallons this time. so I still had 6 gallons still left in the tank.



So 300 divided by 22 gallons gives me 13.6mpg + the 6 gallons I had left over from last fill up



So if I was getting 13.6mpg I would do 13.6 X 6 and get 81.6 and than add that to the 300 to get 381.6 miles I could of drove if I had used the whole 22 gallons (not always true) so we go back and do 381.6 divided by 22 gallons and you get 17.3mpg



I could be doing this all wrong but this is how i get my ROUND about guess...Your never gonna be right on the dot but this gets me somewhere in the ball park.
 
ions,



Are you serious about your math? How much fuel you already had in the tank has no bearing on your mileage. If you drove 300 miles, then filled up with 15 gallons to fill the tank, you only used 15 gallons of fuel the drive 300 miles. Since the tank was full when you started to drive, but you used a certain amount of fuel to drive that distance since there is that much less fuel in your tank. You fill it back up as usual.



So you drove 300 miles on 15 gallons of gas. Do a simple math problem... 300/15=20 MPG since you used 15 gallons to drive 300 miles.



You way, in the same situation, netted you 2.7 MPG less then the actual MPG.





Tom
 
Tracnblack I've never seen that kind of mileage.

A few weeks ago I hit 400 miles on a tank, and topped the tank off with 24 gal. (22.5 gal tank). In reality I was driving on fumes and I wasn't on E yet.

That is when my fuel gauge was screwed up.

I fill up soon after the Low Fuel light alarms, and that is indicative of ~2 gal left in tank.

I normally get around the 17mpg range, burbia driving interleaved with a mix of high freeway speeds.



I go two weeks between fill ups, but there is motorcycle usage in there too.
 
tracn-

That was just an example, numbers pulled from no where. I don't really care about MPG in any way. I get crappy milage, no matter how I drive, so I don't bother to do the math because I don't want to know the result. But, I put in $10 worth of gas a $2.69/gal, drove for an unknown number of miles, and when I got back home, had about the same amount of gas I did before I put gas in.
 
What ions said.



What I do is keep small pad in the glovebox, write down the exact mileage at each fillup and alway fill to the first click-off of the pump and stop, then write down the gallons of gas dispensed. If you do this, then you know how to calculate MPG its:



MPG = ( Current Odometer Reading - Last Odometer Reading ) / Gallons Dispensed





For Example:



Your last fillup:

------------------

Odometer read: 24,732

Gallons dispensed: [don't care]



Your current fillup:

----------------------

Odometer read: 25,003

Gallons dispensed: 20.2



Thus:

------

MPG = ( 25003 - 24732 ) / 20.2

MPG = 13.42 MPG



There was a spreadsheet for calculating MPG, and I think it used a similar scheme. What's nice with this log approach is you can get more accurate measurements over longer periods of time by simply taking two odometer readings further apart and summing all the gas used between them (with the exception of the first...remember, that is paired with the previous two).



Good luck!



TJR
 
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I keep every reciept for gas I get. I write both the trip odometer mileage and the actual mileage. I can check the mileage on the fly, or I could grab a ranger of reciepts and check the mileage over a long range of miles.





Tom
 
Tom. I never said it was right that is just MY WAY of doing it. Do it your way whatever. Also said it got me in the BALL PARK and that is what it does. If I wanted to get a better reading I'd just use my Scangauge.
 
ions,



I know what you said. If a simpler math problem is more accurate, why go through all the work to calculate the mileage if it is so wrong and not even accurate? I know it gets you in the ball park, but there is a difference between a fould ball and a home run, though both can happen in a ball park.



I am not dogging you or anything. I just sometimes wonder why so many people do the things they do.





Tom
 
I just reset the trip odometer each time I fill up and I make sure the tank is full. Then, I just use the mileage on the odometer and however many gallons that show on my receipt. I never get above 18.5 or so, even driving carefully.
 
ion, as long as you it was not coors light and 3 am when you filled the trac you are good to go. I also keep a small book in my console to write down the milage, trip milage,and the gallons, so I can keep up with the gas milage._ I guess I need to post it in the gas milage log online. Ron
 
Number of miles driven divided by the number of gallons I put in. I use the same pump at the same station, unless I'm out of town. I get 20-25mpg on 93 depending on how traffic and other things were that week.
 

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