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Other energy units

Even though the Joule is the official, technical choice of SI-unit for energy,[1] we rarely hear that unit used in daily life. Rather we hear ‘calories’ used in our cook-books, ‘kilowatt-hours’ $\mathrm{kWh}$ used in our electric cars1 and the like.

The reason might be that 1 Joule really does not match many applications very well – its a bit too small for most at the human-scale and a bit too large for most in electronics and the like. Other units that are non-SI might be more convenient in different fields and uses. A few typical non-SI energy units are:

Energy units
Tonne oil equivalent$1\,\mathrm{toe}$$=4.187\times 10^{10}\,\mathrm{J}$Energy in one tonne oil[6]
Kilowatt-hour$1\,\mathrm{kWh}$$=3.6\times 10^6\,\mathrm{J}$Energy spent by using a laptop all day[5]
Calorie$1\,\mathrm{cal}$$=4.19\,\mathrm{J}$Energy in a piece of an m&m2
Electron volt$1\,\mathrm{eV}$$=1.602\times 10^{-19}\,\mathrm{J}$Energy to move an electron through 1 volt[3,1]

In Resource: Often-used units you’ll find even more. Such units have of practical reasons become the mainstream choices in various fields.


  1. Sears and Zemansky’s Univesity Physics with Modern Physics’ (book), Hugh D. Young & Roger A. Freedman, Pearson Education, 13th ed., 2012
  2. Why don't we measure electrical consumption in joules, instead of kWh?’ (web page, forum conversation), Thomas O., Electrical Engineering Stack Exchange, 2011, electronics.stackexchange.com/questions/11452/why-dont-we-measure-electrical-consumption-in-joules-instead-of-kwh (accessed Jun. 12th, 2020)