How to Convert Gasoline Energy to Kilowatt-hours (kWh)

BY Ben Bowlin / POSTED June 14, 2012
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This is our interpretation of people thinking about math. (Lisa Zador/Photodisc/Getty)

The EPA estimates that one gallon of gasoline is equal to 33.7 kWh. But how did they get that number? At first glance, some folks might think this is a pretty intimidating question. But never fear. The conversion of gasoline energy to kWh is surprisingly simple. Here’s how it works.

Let’s start with a measure called the British thermal unit (Btu). A Btu is the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit (or, if you prefer, the amount of heat needed to raise the temperature of 0.45 kilograms of water by 0.56 degrees Celsius). The Btu is a handy starting point for our conversion, because it’s a way to make an apples-to-apples comparison between the energy in a gallon of gas and one unit of kWh.

We know that 1 kWh contains 3,412 Btu.

We also know that 1 gallon of gasoline contains 115,000 Btu.

The rest is just basic division:

115,000 ÷ 3,412 = 33.7 kWh.

Once we’ve got this number, we can use it to convert kWh of electricity to an MPGe that jibes with the MPG of conventional cars. You can learn more about this conversion at the EPA’s website, and check out Scott’s post on MPGe and MPG for more information.

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P.S. – I halfheartedly apologize for that pun in the last sentence.

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