Fuel Economy Calculation for Dummies

fuel economy

There's an old story about the guy who, sick of his neighbor's bragging about his fuel economy, started sneaking over every night for and adding a gallon of gasoline to the neighbor's tank. After a couple of weeks of crowing from the braggart about his increased mileage, the nighttime sneak started siphoning out a gallon each night. So funny... These days, you can't get into the tank of most cars without the keys, so that's not gonna happen... It does, however, bring up the topic of fuel economy and how it's expressed in different countries. That's why we found eHowian Gene Tencza leveraging his BS in industrial education to explain "How to Convert Kilometers Per Liter Into Miles Per Gallon."¹ Never mind that no one uses km/l for fuel economy...

In the Demand Media-mandated introduction (75-100 words), Tencza informs readers that

"In countries that use the metric system, fuel is usually sold by the liter and distances are measured in kilometers. Fuel economy is specified in kilometers per liter. It's easy to convert from kilometers per liter to miles per gallon."

That would be a big "duh," except that in most countries that use the metric system, fuel economy is stated in liters per 100 kilometers (l/100km), not kilometers per liter². Regardless of the units, though, Gene's pretty much right about the "It's easy" part; or it would be if he hadn't made it so damned complex!

Tencza, stuck with a pesky DMS³ "minimum three-step process" breaks the conversion into three steps:

convert kilometers to miles (mi = km * 0.621) convert liters to gallons (gal = l * 0.264) divide miles by gallons In reality, he should have just told his readers to multiply the economy in liters/kilometer by 2.352 to get miles per gallon. Yep: you only need one step, not to mention that you don't need the superfluous "tip" that "If you are converting a "kilometers per liter" value that has been given to you, skip step 2 (the value will always be .264)..."

...which doesn't make all that much sense. For what it's worth, however, the conversion factor we mentioned above (2.352) comes in handy when you want to convert between the typical fuel economy numbers in the metric system, liters per 100km, and MPG. To make that conversion, you divide a conversion factor (235.215) by the known liters/100km value. It may surprise you to note that, while higher MPG values are better, lower l/100km values are better. Do the math...

We had to ponder this particular candidate for a while: Tencza's answer is ultimately correct and he was stuck with that three-step minimum (and minimum word count as well). But he really didn't have to prostitute himself for this post, and that's why we decided he was deserving of today's Dumbass of the Day award. So there.

¹ The original has been deleted by Leaf Group, but can still be accessed using the Wayback machine at archive.org. Its URL was   ehow.com/how_5040989_convert-liter-miles-per-gallon.html
² A team member with broad experience in both metric numbers and autos once attempted to point this out to a higher-up at DMS. He was unsuccessful (that "higher-up" was, of course, a J-school graduate)
³ DMS is Demand Media Studios, parent company of eHow. As we always say around the Antisocial Network, "You can't spell 'dumbass' without 'DMS'!"

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