EcoModder Forum How to calculate MPG / fuel economy formula

Register Now
 Remember

 Submit Tools LinkBack Thread Tools
 12-19-2007, 01:15 PM #1 (permalink) Batman Junior     Join Date: Nov 2007 Location: 1000 Islands, Ontario, Canada Posts: 20,075 Blackfly - '98 Geo Metro Team Metro Last 3: 70.09 mpg (US) MPGiata - '90 Mazda Miata 90 day: 50.45 mpg (US) Winter beater Metro - '00 Chevrolet Metro 90 day: 56.78 mpg (US) Thanks: 2,286 Thanked 5,117 Times in 2,589 Posts How to calculate MPG / fuel economy formula As surprising as it may seem to the hardcore fuel economy nuts who frequent Ecomodder, there are people who have never given much thought to the process of "manually" (ie. without benefit of a ScanGauge or other onboard device) figuring out a vehicle's fuel economy. I had someone ask me how to do it yesterday. After the initial shock wore off I came up with these instructions. Feel free to comment/add suggestions. 1) Next time you get gas, *fill* the tank. You can't calculate mileage if you're in the habit of just adding \$10 or \$20 worth each time. So fill until the pump clicks off once or twice. 2) Reset your trip odometer - if you have one. If you don't have one, write down your current odometer reading. 3) Drive, drive, drive... 4) Next time you need fuel: again, completely fill the tank until the pump stops. Get a receipt. 5) Write on the receipt the distance from your trip odo (or regular odometer) you went since the previous fill up. 6) Divide the distance driven by the amount of fuel used. That's your fuel economy. If your odometer is in miles, and the receipt shows gallons, the resulting number is your MPG (miles per gallon). E.G. let's say you went 360 miles and you completely refilled the tank by adding 8.7 gallons (US). 360 miles / 8.7 gallons = 41.4 MPG. 7) Keep doing this each time you get gas. Save your receipts/calculations in your glove box or wherever. After a few fill-ups you'll be able to see what's "normal" for your car (assuming you do the same type of driving for each tank), and you can start using this info as a baseline from which you can try to improve. __________________ Latest mods test: 15 mods = 15% MPG improvement: A-B test, 2007 Honda Civic 1.8L, 5-speed Ecodriving test: Manual vs. automatic transmission MPG showdown: Nissan Micra 1.6L EcoModder has launched a forum for the efficient new Mitsubishi Mirage www.MetroMPG.com - fuel efficiency info for Geo Metro owners www.ForkenSwift.com - electric car conversion on a beer budget
 Today Popular topics Other popular topics in this forum... View the most popular topics in this subforum by views or by posts
12-19-2007, 01:25 PM   #2 (permalink)
ECO-Evolution

Join Date: Nov 2007
Location: Central Texas
Posts: 1,482

Iron Horse (retired) - '97 Iron horse Intrepid

Ninja - '08 Kawasaki 250R
90 day: 76.23 mpg (US)
Thanks: 17
Thanked 42 Times in 32 Posts
Quote:
Originally Posted by MetroMPG
1) Next time you get gas, *fill* the tank. You can't calc mileage if you're in the habit of just adding \$10 or \$20 worth each time. So fill until the pump clicks off once or twice.
Quote:
 Whichever you choose do it the same every time
4) Next time you need fuel: again, completely fill the tank until the pump stops. Get a receipt.
Quote:
 1 or 2 clicks whatever you decided on
Might want to say something about a shortfill not being accurate and once you have the FE bug try to use the same pump for every fill.
__________________
"Judge a person by their questions rather than their answers."

Last edited by Lazarus; 12-19-2007 at 01:28 PM.. Reason: short fill

 12-19-2007, 04:49 PM #3 (permalink) Batman Junior     Join Date: Nov 2007 Location: 1000 Islands, Ontario, Canada Posts: 20,075 Blackfly - '98 Geo Metro Team Metro Last 3: 70.09 mpg (US) MPGiata - '90 Mazda Miata 90 day: 50.45 mpg (US) Winter beater Metro - '00 Chevrolet Metro 90 day: 56.78 mpg (US) Thanks: 2,286 Thanked 5,117 Times in 2,589 Posts Good points. For "moderate" fuel economy types. You will know you've gone hardcore when you proceed to step 8: validating your odometer's accuracy and adding a correction factor in all your MPG calculations because it drives you nuts that it was off by 1.5% __________________ Latest mods test: 15 mods = 15% MPG improvement: A-B test, 2007 Honda Civic 1.8L, 5-speed Ecodriving test: Manual vs. automatic transmission MPG showdown: Nissan Micra 1.6L EcoModder has launched a forum for the efficient new Mitsubishi Mirage www.MetroMPG.com - fuel efficiency info for Geo Metro owners www.ForkenSwift.com - electric car conversion on a beer budget
12-19-2007, 05:30 PM   #4 (permalink)
EcoModding Apprentice

Join Date: Dec 2007
Location: Melbourne
Posts: 152

The Mighty Mira - '92 Daihatsu Mira
90 day: 61.32 mpg (US)
Thanks: 0
Thanked 7 Times in 7 Posts
Quote:
 Originally Posted by MetroMPG You will know you've gone hardcore when you proceed to [B]step 8:
And I thought I was OCD. I'm just comparing to myself, basically, so I have skipped this step.

I like to do l/100km, so I just divide the other way, the number of litres by the number of kilometres (on my phone calculator), then shift the decimal point until it makes sense (two places).

The only problem with hypermiling is that it takes longer to get accurate feedback this way!
__________________
"Every body perseveres in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed." - Isaac Newton

12-27-2007, 02:27 AM   #5 (permalink)
Modding for Eris

Join Date: Dec 2007
Location: North Bay, Ontario, Canada
Posts: 129

SilverCivic - '08 Honda Civic
90 day: 28.69 mpg (US)
Thanks: 39
Thanked 11 Times in 8 Posts
I've been doing this for a little while now (though the car was off the road for a couple of months, so there's a hole in my figures) and it's quite interesting to see the trends.

I've been using a OO spreadsheet to track distance, fuel usage, cost, time between fillings, km/L etc, as well as the differences between values. Probably too many things, really, but it is interesting.

Here's the spreadsheet. Only seven entries so far, so the averages aren't the most accurate. And the numbers are all metric, and australian dollars. But it might be a handy template for someone else.

The EV bits on the right end are based on figures I've gotten around the intarwebs for comparison - one of these years I'll convert a car to electricity and test it out myself.

The file is .ods for Open Office, I can provide an .xls version if asked.
Attached Files
 Fuel Use Spreadsheet.zip (15.6 KB, 234 views)
__________________
Making do with a Honda Civic. Tesla Model 3 reserved. Still kinda want an SVX for fun, though.

 11-13-2008, 10:46 AM #6 (permalink) Master EcoModder   Join Date: Jun 2008 Location: London, Ontario Posts: 1,096 2k2Prot5 - '02 Mazda Protege5 90 day: 33.82 mpg (US) Thanks: 0 Thanked 11 Times in 8 Posts Ever since i signed up here I have been writing the mileage on my receipt and stuffing it into the glove box. One day I will actually pull them all out and enter them into the fuel log... i wanted to ignore it for a while so i could get a good back-trend. Maybe its that time.
 11-13-2008, 11:38 AM #7 (permalink) EcoModding Apprentice   Join Date: May 2008 Location: Bono, AR Posts: 170 Daily Driver - '01 Ford Explorer Sport 90 day: 18.12 mpg (US) Thanks: 0 Thanked 1 Time in 1 Post i love using excel to do all the work for me. heres what i do: lets start at line 5 A5 is where i enter the date B5 is my calculated gas mileage -enter " =D5/F5 " without the quotes C5 is where i enter my trip OD miles for that tank D5 is my "miles adjusted for tire size" formula (takes info from C5, its also the cell used for B5) E5 calculates my cost per gallon (to keep from having to enter it myself every time) -enter " =G5/F5 " F5 is where i enter my gallons pumped G5 is where i enter total fill-up cost H5 calculates "cost per mile" for me. -enter " =G5/D5 " I5 is for notes if you don't have mileage correction, just skip that one, and move your formulas over accordingly. once you enter the formulas a few times (remember to change the number to whatever line you are on, and letters stay the same), excel recognizes the pattern and fills in for you. i also did different width borders, put the mpg in bold text, and some other little things. i need to print it out and scan it as a .jpg, so i can post it up as a picture. once its all set up, and remembers the pattern, keeping up with it is a piece of cake. i just fill-up, enter miles on the receipt, enter info into my computer, and throw the receipt into the recycle bin at work. btw, the "cost per mile" has been really informative, almost more than mpg. when gas prices hit their summer/fall peak, i was getting my best mpg, and it was costing me .20 a mile to drive. now that the weather has gotten colder, my mpg have fallen. but so have gas prices. now i'm paying .10 a mile __________________ My Intro Last edited by Tony Raine; 11-13-2008 at 11:47 AM..
 11-13-2008, 05:46 PM #8 (permalink) Master EcoModder     Join Date: Jun 2008 Location: North Andover, MA Posts: 857 Bone's 2010 Prius - '10 Toyota Prius Black 90 day: 56.78 mpg (US) Thanks: 5 Thanked 20 Times in 16 Posts Prior to getting my scanguage (just a couple weeks ago) I had been filling the tank past when the pump clicks (as much as 1 to 1.5 gallons). Now I am using the same pump, same station and only fill until it clicks. I suspect this will more accurately represent my mpg as filling past the click could be off by as much as half gallon every time I fill depending on how much time I spend trying to get it to max fill. The only reason I filled past the click was to get another 2-3 days of driving in before having to fill up. With only an 8 mile roundtrip commute for work the fill past click saves a stop once or twice a month. But, to keep my sg2 accurate I'm just going to the click now. __________________ My Facebook: http://www.facebook.com/home.php?#/p...?id=1268001941 My Twitter: http://twitter.com/bone1124
 12-03-2008, 03:16 PM #9 (permalink) C12 H23 burner     Join Date: Jul 2008 Location: Granby, Qc, Canada Posts: 21 Jeece's Jetta - '99 Volkswagen Jetta GL TDI 90 day: 42.49 mpg (US) Thanks: 0 Thanked 2 Times in 1 Post Since I got my current car 1 year ago, I also log all my fuel receipts in a spreadsheet (found elsewhere). As with the above MPG formula, consistency is key - always fillup to the same point. So far I always forgot to write down the Current tank average on my ScanGauge before I reset it, so I can't compare its precision with the spreadsheet. Oh well, next tank, or the one after. __________________
12-03-2008, 03:19 PM   #10 (permalink)
MechE

Join Date: Dec 2007
Location: Bay Area
Posts: 1,151

The Miata - '01 Mazda MX-5 Miata
Thanks: 0
Thanked 18 Times in 15 Posts
Quote:
 Originally Posted by Jeece So far I always forgot to write down the Current tank average on my ScanGauge before I reset it, so I can't compare its precision with the spreadsheet. Oh well, next tank, or the one after.
I do the same thing I'm always too excited to see what the error is, that I forget to write it down

__________________
Cars have not created a new problem. They merely made more urgent the necessity to solve existing ones.

 Thread Tools

 -- EcoModder Skin -- Mobile / Lightweight skin Contact Us - EcoModder.com - Archive - Recent Posts - Top

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com