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Old 12-19-2007, 01:15 PM   #1 (permalink)
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Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,521

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 52.71 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)

Appliance car - '14 Mitsubishi Mirage ES (base)
90 day: 52.48 mpg (US)
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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.

Project MPGiata! Mods for getting 50+ MPG from a 1990 Miata
Honda mods: Ecomodding my $800 Honda Fit 5-speed beater
Mitsu mods: 70 MPG in my ecomodded, dirt cheap, 3-cylinder Mirage.
Ecodriving test: Manual vs. automatic transmission MPG showdown

has launched a forum for the efficient new Mitsubishi Mirage - fuel efficiency info for Geo Metro owners - electric car conversion on a beer budget
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