# Explain "energy density" of fuels
**URL:** https://boards.straightdope.com/t/explain-energy-density-of-fuels/253079
**Category:** Factual Questions
**Created:** [July 1, 2004, 5:03pm UTC](https://boards.straightdope.com/t/explain-energy-density-of-fuels/253079 "2004-07-01T17:03:29Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@hammerbach](https://boards.straightdope.com/u/hammerbach)
#### Post date: [July 1, 2004, 5:03pm UTC](https://boards.straightdope.com/t/explain-energy-density-of-fuels/253079/1 "2004-07-01T17:03:29Z")
I want to be sure I know what is meant when I hear about “energy density”. Using units I’m familiar with, I found that Diesel has a density of about .0415 kW per gallon. I would take that to mean that if I could convert the chemical energy in a gallon of Diesel fuel directly into electrical energy, with 100% efficiency, I could only get .0415 kW-hours out of it. That seems ridiculously low… Can someone tell me where I’ve been a bonehead here?
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### Author:  [@Nametag](https://boards.straightdope.com/u/Nametag)
#### Post date: [July 1, 2004, 5:35pm UTC](https://boards.straightdope.com/t/explain-energy-density-of-fuels/253079/2 "2004-07-01T17:35:35Z")
I don’t know where you made your mistake, but you’re off by a factor of 1000.
38.5 x 10[sup]9[/sup] J/m[sup]3[/sup] x 10[sup]-3[/sup] m[sup]3[/sup]/L = 38.5 x 10[sup]6[/sup] J/L
38.5 x 10[sup]6[/sup] J/L x 10[sup]-3[/sup] kW-s/J = 38.5 x 10[sup]3[/sup] kW-s/L
38.5 x 10[sup]3[/sup] kW-s/L ÷ 3600 s/hr = 10.7 kW-hr/L
10.7 kW-hr/L x 3.785 L/gal = 40.5 kW-hr/gal
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [July 1, 2004, 5:39pm UTC](https://boards.straightdope.com/t/explain-energy-density-of-fuels/253079/3 "2004-07-01T17:39:38Z")
According to [url=http://www.vr-transport.de/transrapid-energy/n003.htmlthis page, diesel has an energy density of 9.8 kWh/l or roughly 39 kWh/gal., which seems more reasonable to me. On preview, this agrees well with **Nametag** ’s figure.
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### Author:  [@hammerbach](https://boards.straightdope.com/u/hammerbach)
#### Post date: [July 1, 2004, 5:47pm UTC](https://boards.straightdope.com/t/explain-energy-density-of-fuels/253079/4 "2004-07-01T17:47:17Z")
Thank you. Must be a conversion error somewhere. So, energy density is what I think it is, then? Thank you very much.
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [July 1, 2004, 5:52pm UTC](https://boards.straightdope.com/t/explain-energy-density-of-fuels/253079/5 "2004-07-01T17:52:15Z")
> [@hammerbach](#):
>
> So, energy density is what I think it is, then?
Yep, pretty much. It’s just the amount of chemical energy available per unit of fuel; a convenient figure for comparing various fuels and their costs, and such.
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### Author:  [@hammerbach](https://boards.straightdope.com/u/hammerbach)
#### Post date: [July 1, 2004, 6:01pm UTC](https://boards.straightdope.com/t/explain-energy-density-of-fuels/253079/6 "2004-07-01T18:01:03Z")
I’m very comforted to know it’s merely my late-night arithmetical skills that are atrocious :smack: , and not my general grasp.
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### Author:  [@KP](https://boards.straightdope.com/u/KP)
#### Post date: [July 1, 2004, 7:49pm UTC](https://boards.straightdope.com/t/explain-energy-density-of-fuels/253079/7 "2004-07-01T19:49:51Z")
Let me guess: you were converting from table values in calories. The factor of 1000 makes me suspect that the small **c** alorie/large **C** (kilocalorie) convention got you. In fact, you may not have made any mistake at all. I’ve seen tabular compilations that gave mistaken values, esp when converting diverse sources to a common unit, like joules/L or kWh/kg. The calorie capitalization convention is far from universal, and many editors refuse to use it. Alas, this doesn’t allow them to ignore it – they must still be eagle-eyed about the units/conventions used in each source.
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### Author:  [@hammerbach](https://boards.straightdope.com/u/hammerbach)
#### Post date: [July 2, 2004, 5:05am UTC](https://boards.straightdope.com/t/explain-energy-density-of-fuels/253079/8 "2004-07-02T05:05:19Z")
Good guess, but not quite… I was trying to work out kWh/pound (to evaluate someon’s claims, which I can’t discuss here), with many merry adventures through units both imperial and metric, and lost it between grams and kilograms. Right factor, wrong unit. It was a late night.