Energy and Work Converter

Convert joules, calories, kilocalories, kWh, BTU and electronvolts.

Popular energy conversions

calories to kilojoules kilojoules to calories

Energy unit reference chart

What one of each unit is worth in joules, the base unit used for every conversion in this category.

Energy units expressed in joules
Unit	Symbol	1 unit in J
joules	J	1 J
kilojoules	kJ	1,000 J
calories	cal	4.184 J
kilocalories	kcal	4,184 J
kilowatt hours	kWh	3,600,000 J
watt hours	Wh	3,600 J
British thermal units	BTU	1,055.055853 J
foot-pounds	ft·lb	1.355817948 J
megajoules	MJ	1,000,000 J
electronvolts	eV	1.602176634e-19 J
therms	thm	105,505,585.3 J
ergs	erg	0.0000001 J

Energy units explained

Joules (J)

The joule is the SI unit of energy: the work done by a force of one newton acting over one meter.

Kilojoules (kJ)

The kilojoule is 1,000 joules and is the food-energy unit on nutrition labels outside the United States.

Calories (cal)

The thermochemical calorie is defined as exactly 4.184 joules. Note that the “calories” on food labels are actually kilocalories.

Kilocalories (kcal)

The kilocalorie, written kcal or capital-C Calorie, is 1,000 thermochemical calories — the unit meant by “calories” on food packaging.

Kilowatt hours (kWh)

A kilowatt hour is the energy used by a 1,000-watt device running for one hour: exactly 3.6 megajoules. It is the unit on electricity bills.

Watt hours (Wh)

A watt hour is exactly 3,600 joules — the energy used by a one-watt device in one hour. Battery capacity is rated in watt hours.

British thermal units (BTU)

The BTU is the energy needed to raise one pound of water by one degree Fahrenheit — about 1,055 joules. It rates heating and air-conditioning equipment in the US.

Foot-pounds (ft·lb)

A foot-pound is the work done moving one pound-force through one foot: about 1.356 joules. The same name is also used for torque, where the newton-metre is the metric equivalent.

Frequently asked questions

What is the base unit of energy?

This converter routes every energy conversion through the joule. Converting from one unit to another means converting to joules first and then out again, which keeps every pair consistent with every other pair.

How accurate are these energy conversions?

Results are shown to 10 significant digits using exact defined factors wherever a unit has one. No rounding is applied beyond that final display step.

All energy conversions

Every energy conversion page on this site, 84 in total.