A joule is the SI base unit for energy. It is equal to [math]1 \frac{kgm^2}{s^2}[/math].[1] In physical terms, lifting an apple one meter takes 1 joule of energy. This should not be confused with a watt which is a unit of power and a rate of how fast energy is used.

While the joule is the SI base unit for energy, when speaking in real-world terms, we often use the kilowatt-hour (kW/hr) instead. This is due to the fact that a joule is an extremely small amount of energy. To put how small a joule is into perspective, a liter of gasoline has 31,536,000 joules of energy in it. A kilowatt-hour is equal to 3,600,000 joules. Therefore, a liter of gasoline has 8.76 kW/hr of energy in it, which is a much more manageable number.


To read more about the Joule, click here

For Further Reading


  1. APS Physics. (2015). Energy Units [Online]. Available: [February 20, 2015].

Authors and Editors

Allison Campbell, Jordan Hanania, James Jenden, Kailyn Stenhouse, Jason Donev
Last updated: June 25, 2018
Get Citation