How to Calculate Miles Per Gallon - Toyota Tundra Forums : Tundra Solutions Forum
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post #1 of 1 (permalink) Old 11-26-2010, 06:44 PM Thread Starter
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How to Calculate Miles Per Gallon

I cannot begin to tell you how often I hear a generalized statement about someone's fuel economy. It usually goes something like this: "I am getting around XXX miles per tank of gas." It is the non-exact nature of this statement that leads to serious misunderstandings about what kind of fuel economy you think you should be getting with your vehicle or what your perception is of someone else's fuel economy with their vehicle. More often than not these "tank-gestimates" are way off from the actual mileage that person is getting.

Then there are those who rely on the trip computer in their vehicle to tell them how many miles per gallon they are getting. This method is more accurate than the generalized statement of “XXX miles per tank of gas.” Even so, unless you are able to input the diameter of your tires even this method can be off by a mile or so per gallon.

Another version of the trip computer is the Scan Gauge. This is a highly accurate instrument that monitors a broad spectrum of the conditions that affect vehicle performance. The Scan Gauge is a great tool for understanding how your vehicle is performing under real time conditions. In order to return the most accurate figures the tire diameter of your vehicle must also be entered into the Scan Gauge. You can learn more about the Scan Gauge from their website

ScanGaugeII - Trip Computers + Digital Gauges + Scan Tool

The tried and true method for those of us without the benefit of a trip computer or Scan Gauge is the old pen, paper, and calculator. I recommend this even for those who do have a trip computer or Scan Gauge as it is an excellent way to verify if you are getting accurate results from those devices. Here is how I recommend to do it:

  1. Try to fill up from the same gas pump. By doing this you reduce the variables associated with different pumps.
  2. Use the same octane gas each time. If you switch octane the ECU (Engine Control Unit) will try to compensate for this and your results will be inconsistent. Switching to a higher octane gas may yield initial improvements but the ECU will adjust for this and the mileage will return to its original (pre-higher octane) numbers. In order to establish solid fuel economy numbers it is necessary to do this for at least ten tanks of fuel. Notice I said ten tanks and not ten fill-ups.
  3. Start off by filling up. Where possible use a pump with an automatic shut-off nozzle. This is the kind where you put the nozzle in the tank, squeeze the handle and it pumps by itself and shuts off automatically when the tank is full. If you do not have access to a pump with an automatic shut-off handle then you get to hold the handle yourself until it stops.
  4. When the pump stops, turn off the pump, squeeze the handle to get the last few drops out of the hose, and put the nozzle back in its holster.
  5. Get your receipt and double check it against the read out on the pump.
  6. Turn your ignition key until you get a readout on your trip odometer then write the number of miles on the back of the receipt.
  7. Zero the odometer and then start your vehicle.
  8. When you get home, divide the number of miles (xxx.x) by the number of gallons ( and this will give you your miles per gallon.
  9. Repeat these steps each time you fill up with gas.

Instead of number 8 above, you can join Fuelly | Share and Compare Your MPG and track your numbers there. It is free and keeps track of your fuel economy and even graphs your mileage fill-up to fill-up.

In order to get a good, solid baseline number for your fuel economy you need to do this each time you fill up for at least ten tanks of fuel. Doing so over a longer period of time serves to even out any inconsistencies and returns more accurate numbers.

[Use by author permission from]

355,164 miles on the odometer [come see me when you get that on your ford]

2004 Tundra Double Cab Limited Edition 4.7 liter V8, four speed automatic, four wheel drive, testing platform for fuel economy, Ultragauge, Long Tubes with x-pipe and true duals,stock intake, Mobile 1 in the engine, NAPA oil filter, NAPA [COLOR=Black]in the differentials. 3:91 gears in the front and rear [SIZE=2]differentials, Cooper Discover ATP tires

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