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Standard: SI derived unit
Quantity: Energy
Symbol: J
Named after: James Prescott Joule
Expressed in: 1 J =
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

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.

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.