Once upon a time you may have thought you knew what kind of gas mileage you were getting with your car, SUV or truck. It was a question you asked when you were shopping, and only when you were shopping. Perhaps you even made the assumption that you never needed to calculate mileage again so you forgot about it.

When you bought your car you found out that your kind of make and model of vehicle had an EPA rating of XYZ miles per gallon (mpg) Autel MaxiPRO MP808TS. Off you drove, secure in the knowledge that since you were getting XYZ miles per gallon and you had a 14 gallon tank (the average size now), you would need to fill up every ABC miles and it should cost you DEF.

Oh for the days of DEF! Or even for the days of just driving ABC miles. The average American now faces a 29 mile round trip commute to work. In addition to living further away from where we worked 50 years ago, we also live further away from the grocery store, our children's playmates, and where we go to relax and unwind after work.

Until the end of 2007, we could at least take heart in the fact that the XYZ miles per gallon part of our calculation remained the same. All that changed in January, 2008.

That's when the Environmental Protection Agency's (EPA) new gas mileage calculators went into affect. It's the first time the numbers have changed in more than 20 years.

Over those twenty years minor fluctuations in values evened out and the EPA was left with solid evidence that led them to include and weight certain factors in their formulas differently than the original numbers autel online.

Three factors in particular made a big impact on the changed numbers. The effects of colder outside temperatures in the winter and running your air conditioner to create colder inside temperatures in the summer were added to gas mileage calculators for the first time. Faster accelerations and faster driving speeds overall than had previously been calculated were also added to the calculations.

These are not the only factors that go in to the EPA ratings. That's why the EPA continues to remind everyone that "your mileage may vary." In fact, some of the other criteria they look at could

How and where you drive and the overall condition of your vehicle are also key. Fuel variations, vehicle variations, and age of your vehicle are also important. For example, that "sports car package" of options you purchased that put that great looking spoiler on your trunk could also be spoiling your mpg rating compared to cars that are otherwise identical but don't have the spoiler.

To quickly see how the change affects you, when you visit the gasmileagecalculators.com website, you can use a free tool to simply convert the old EPA rating for the vehicle make and model you select to the new one.

Calculating this difference is just the first step in determining what your gas mileage rating really is. It will give you a ballpark figure of what you can expect only. To get the more accurate reading of your mileage that you need to read our post entitled "Two Methods to Calculate Your Gas Mileage."

Liz Micik is a freelance writer on alternative fuel sources who shares the gas mileage calculators ordinary people use to save thousands in gas costs every year
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