SI unit of energy, work and amount of heat

A joule (/ˈl/ or sometimes /ˈl/) is a unit in the SI system. It measures energy; usually in scientific or electrical appliances . It is named after James Prescott Joule.

Unit systemSI derived unit
Unit ofEnergy
Named afterJames Prescott Joule
1 J in ...... is equal to ...
   SI base units   1 kg·m2/s2
   CGS units   1×107 erg
   kilowatt hours   2.78×10−7 kW⋅h
   kilocalories   2.39×10−4 kcal
   BTUs   9.48×10−4 BTU
   electronvolts   6.24×1018 eV

A joule refers to the amount of energy transferred to an object when a force of 1 newton is applied on it over a distance of 1 metre (1J = 1N × 1m). It is related to the watt (a unit of power): one watt equals one joule per second.

It can also be understood as the work done for passing one ampere of electric current through an electric circuit of external resistance equivalent to one ohm for one second.