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Physicists measure energy in joules, because a joule is based entirely on metric units kg * m2 / s2. But a joule is a bit too small for the kinds of calculations we do on this wiki.

Here are some other energy units for comparison:

Unit Joules Note
watt second 1 Electrical power is often measured in watts. A watt is the same as 1 joule per second.
calorie (lowercase) 4 This is not the unit for measuring food. This is an old outdated unit.
(show formal definition)|The amount of energy needed to heat 1 gram of water up by 1 degree Celsius.
kilojoule 1,000
BTU 1,055 British Thermal Unit (used for heating, typically).
watt hour 3,600 Used in battery specs.



Calorie (uppercase)
4,184 This is the unit used for measuring food energy.

For example, "A diet of 2000 Calories" (which would be 8,368,000 joules).

(show formal definition of unit)|The amount of energy needed to heat 1 kilogram of water up by 1 degree Celsius.
megajoule 1,000,000
kilowatt hour 3,600,000 Used on electricity bills.
gallon gasoline 131,881,980 The amount of energy you'd get from burning 1 gallon of gasoline.
gigajoule 1,000,000,000 Enough energy to power a house for a week or two.
terajoule 1,000,000,000,000
petajoule 1,000,000,000,000,000 Enough energy to power 32,000 homes for a year.
Mtoe 41,868,000,000,000,000 The energy in 1 million tons of crude oil.
exajoule 1,000,000,000,000,000,000
quad 1,055,055,900,000,000,000 A quadrillion BTU (see unit defined above)
CMO 160,000,000,000,000,000,000 Cubic mile of oil. This is approximately how much energy the world uses in every 3 to 4 months.

If you want to do more conversions or calculations, you can use the calculator.