Quick example
Convert 1 kWh to joules
One watt is one joule per second, and one hour contains 3,600 seconds. A kilowatt-hour therefore equals 1,000 watts multiplied by 3,600 seconds, or exactly 3,600,000 joules.
Quick reference
Common energy conversions
| Starting energy | Equivalent |
|---|---|
| 1 kJ | 1,000 J |
| 1 Wh | 3,600 J |
| 1 kWh | 3,600 kJ |
| 1 kWh | 3,412.14 BTU |
| 1 cal | 4.184 J |
| 1 kcal | 4,184 J |
| 1 BTU | 1,055.06 J |
| 1 ft⋅lbf | 1.35582 J |
Unit definitions
Electrical, thermal, food, and mechanical energy
Joules and watt-hours
The joule is the SI energy unit. Watt-hours measure the energy transferred by a given power over time; one Wh is exactly 3,600 J.
Calories and kilocalories
This tool uses the thermochemical calorie of exactly 4.184 J. A food Calorie is one kilocalorie, or exactly 4,184 J.
International Table BTU
The BTU option uses the International Table definition of 1,055.05585262 J, common in heating and energy specifications.
Foot-pound-force
A foot-pound-force is the work done by one pound-force through one foot and equals approximately 1.355817948 J.
Energy versus power
Watts are not watt-hours
Power is the rate at which energy is transferred; energy is the total amount transferred. Converting watts to watt-hours requires a time duration, so watts are not included as a standalone energy unit. This converter accepts negative values for signed work or energy changes but does not infer what the sign means for a particular system.
Common questions
Energy conversion FAQ
How many joules are in one kilowatt-hour?
One kilowatt-hour equals exactly 3,600,000 joules.
How many BTU are in one kilowatt-hour?
One kilowatt-hour equals approximately 3,412.1416 International Table BTU.
Is a food Calorie the same as a calorie?
A food Calorie with a capital C is one kilocalorie, equal to 1,000 thermochemical calories or exactly 4,184 joules.
What is the difference between watts and watt-hours?
Watts measure power, or the rate of energy transfer. Watt-hours measure energy. A 1,000-watt device running for one hour uses 1 kilowatt-hour.
Can energy values be negative?
Energy consumption totals are usually nonnegative, but energy changes and signed work can be negative depending on the chosen system and direction.