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So What's An 'MPGe' Anyway? Ford Explains It All For You

 
1,978 views Oct 12, 2012
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If you've been looking at buying a new electric car, you'll have noticed a slightly different measurement of economy on the official labels: MPGe.

But what does MPGe actually mean? Luckily, Ford is here to help you, so check out the video above to learn more.

Effectively, MPGe is a measure that lets consumers compare the familiar measure of fuel economy in gasoline and diesel cars--miles per gallon--with the very different energy use of electric cars.


Normally measured in kilowatt-hours (kWh), it isn't always easy to see how much of a benefit you might be getting by running an electric car.

Luckily, the U.S. Department of Energy's Argonne National Laboratory has measured the energy in gasoline, and deduced that one gallon of gasoline contains the equivalent of 33.7 kWh of electricity.

Once you can compare the two, it's a simple matter of converting the energy use of a given electric car into a figure in miles per gallon--even though no fossil fuel is being burned in the car.

That's how the 2012 Nissan Leaf's 34 kWh/100 miles is converted to 99 MPGe, and Ford's Focus Electric gets 105 MPGe combined from its 32 kWh/100 miles efficiency.

Some vehicles, like plug-in hybrids, get both MPGe and regular MPG measurements, to describe their efficiency both in electric vehicle mode, and in traditional hybrid mode.

For more, check out Ford's video--and leave any thoughts in the comment section below.

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Comments (14)

  1. fb_1001015277 avatar John Briggs Posted: 10/12/2012 5:37am PDT

    Next up, explain the MPGe of a blended mode hybrid like the plug-in Prius and the Ford C-Max and why the C-Max is better because of the higher speed electric mode and the longer e-range.

    My head hurts already. "Math is hard" as Barbie says.
     
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  2. fb_615350351 avatar Nick Willan Posted: 10/12/2012 10:28am PDT

    MPGe is a decent metric but many people use MPG to determine the COST of driving the car per mile.

    Without taking into account the cost of electricity vs cost of gasoline, MPGe doesn't tell you the full story of the cost per mile.

    I pay $0.06/kWh (Ontario, off-peak). So my cost per gallon equivalent (For my make-believe Tesla) is $2.022 (0.06 * 33.7). It's rated at around 90 MPGe. Factor in the cost per gallon equivalent of electricity and it's like driving a car with 180 MPG (based on $4 gallon). Or more like 225 MPG with $5/gallon.

    Everyone pays different amounts for gas and electricity but I just thought I'd point out that MPGe doesn't really tell you the whole story when it comes to cost/mile.
     
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  3. fb_1001015277 avatar John Briggs Posted: 10/13/2012 11:15am PDT

    Fortunately the EPA already puts the operating cost savings in the window of every car sold in the USA. This cost savings is the second largest font on the windows sticker after MPGe.
     
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  4. robok2 avatar robok2 Posted: 10/12/2012 12:32pm PDT

    If one is careful, I'd say MPGe can be useful, but of course, it's not always comparing apples to apples, etc... I do think there are better ways to express data but I don't have a problem with it overall. The current controversy on GCR regarding it is interesting to me, but not that critical since I just use other metrics (cost, in many cases) if I don't think MPGe is a valid comparison point.

    But I'm not concerned about most readers here, who are generally knowledgeable about these issues. I want whatever is easiest for non-EV fans so they, too, can understand, why EVs and EREVs make sense in many cases. In that sense, MPGe is tolerable, I guess, if not ideal.
     
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  5. fb_1559222512 avatar Xiaolong Li Posted: 10/12/2012 2:42pm PDT

    It is easier to compare EV's MPGe vs. regular hybrid and ICE's MPG.

    For cars such as Volt, C-Max/Fusion Energi or to some extend the Prius Plugin, it heavily depends on how the car is driven (EV vs extended range). Things will get a bit muddy...
     
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  6. Jiminy avatar Jim Royston Posted: 10/12/2012 6:32pm PDT

    I think MPGe as a measure sucks. To suggest that a hybrid car sometimes propelled by gasoline is slightly more efficient than a fully electric car is misleading and does not adequately convey the potential cost per mile disparity between the two. A Leaf is way cheaper to run than a plug-in hybrid if gasoline is used.
     
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  7. Jiminy avatar Jim Royston Posted: 10/12/2012 6:49pm PDT

    Also wanted to mention that I am not anti-PHEV. I just don't think MPGe is at all useful for comparing PHEV or EREV against straight EV's.
     
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  8. fb_1001015277 avatar John Briggs Posted: 10/13/2012 11:21am PDT

    Fortunately, the EPA displays the yearly cost to run each vehicle right on the window sticker.

    For example, the LEAF is listed as costing $600 per year to fuel versus $1150 per year for the Prius. So the LEAF is roughly half the cost to fuel as the Prius.

    On the other hand, if you had to pay MSRP for both vehicles, the Prius would be cheaper, overall.

    On the third hand, Given government incentives and a currently motivated Nissan sales force, the LEAF might come out a winner.

    In the end, some how, I don't feel that the cost of fueling will be the deciding factor between the LEAF and the Prius. Owners likely want an EV for other reasons than squeezing pennies.
     
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  9. Jiminy avatar Jim Royston Posted: 10/12/2012 6:59pm PDT

    Not to beat a dead horse but is the 33.7kWh per gallon of gasoline number derived from pure gasoline or the 10% ethanol stuff they are pushing on us now? Seems like it would make a difference. cars powered with gasoline will get less MPGe on 10% ethanol gas than on pure gasoline. What are the numbers based on? If the assumption is pure gas then the MPGe is even more of a farce if short range PHEVs are compared with pure EV's or cars run as pure EV's like some Volts.
     
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  10. fb_1559222512 avatar Xiaolong Li Posted: 10/12/2012 11:30pm PDT

    I agree.

    They should use Miles/KWh as efficiency gauge for cars such as Volt/EREVs and EVs.

    Leave the MPG to hybrids and regular gas cars.

    As far as plugin goes, it should list the EV mode and hybrid mode seperately.
     
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  11. fb_1001015277 avatar John Briggs Posted: 10/13/2012 11:11am PDT

    I think the reason for the MPGe is that the EPA wanted a method to express the efficiency over a range of alternative drive trains. If two fuels (like electricity and gasoline) will be blended during one trip, I don't see much alternative.

    You could also make an argument for computing diesel efficiency in terms of MPGe. Since diesel starts with more energy per gallon, its MPGe would be less than its posted mpg.
     
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  12. fb_100001502216955 avatar Scott Hubbard Posted: 10/14/2012 5:57am PDT

    The impression I get is that MPGe is calculated based on all of the energy in a gallon of gasoline. Is that correct? I'm curious because, I'm aware that ICE engines only use less than 30 percent of the energy available in gas. Just curious about how the comparison works from a pragmatic point of view. Thanks
     
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  13. john_v avatar John Voelcker Posted: 10/14/2012 6:25am PDT

    @Scott: Yes, it is the distance (in miles) an electric car can travel on the energy content (in kWh) contained in one gallon of gasoline.

    Electric drive is far more efficient than gasoline engines, as you note, which waste roughly three-quarters of that energy content in heat and noise.
     
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  14. fb_1001015277 avatar John Briggs Posted: 10/15/2012 5:03am PDT

    Importantly, what MPGe does NOT include is the inefficiency of the power plant that created the electricity. If the electricity comes from coal or natural gas, than electric cars are not as impressively efficient. That is the conversion from a primary source fuel (e.g. coal) to miles, is not much better in an EV than a hybrid.

    On the other hand, EVs can be powered by renewables like wind and solar so represent a truly sustainable option for the future in a way that gas cars do not.
     
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