Energy converter
Type an energy, choose the units, and see the result and the same energy in every common unit. Food Calories, kilowatt-hours and BTU all have exact definitions in joules.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Type a number. A dot or a comma works as the decimal separator.
- Choose the unit you have and the unit you need. The ⇄ button swaps them.
- The table below shows the same energy in all common units at once.
Conversion factors
Every unit is converted through the joule.
| Unit |
In joules |
| 1 watt-hour (Wh) |
3,600 J |
| 1 kilowatt-hour (kWh) |
3,600,000 J |
| 1 calorie (cal, thermochemical) |
4.184 J |
| 1 kilocalorie (kcal, food Calorie) |
4,184 J |
| 1 BTU (International Table) |
1,055.05585262 J |
| 1 foot-pound force |
1.3558179483 J |
| 1 electronvolt (eV) |
1.602176634 × 10⁻¹⁹ J |
Worked example
A daily intake of 2,200 kcal is 2,200 × 4.184 = 9,204.8 kJ. A heater using 1.5 kWh uses 1.5 × 3.6 = 5.4 MJ, or 1.5 × 3,412.14 = 5,118 BTU.
Quick reference
- 1 kcal ≈ 4.184 kJ ≈ 3.968 BTU
- 1 kWh = 3.6 MJ ≈ 860.4 kcal
- 1 BTU ≈ 1.055 kJ ≈ 0.2931 Wh
- 1 kJ ≈ 0.239 kcal
Frequently asked questions
How many kilojoules are in a kilocalorie?
4.184. Food labels in the US list "Calories" (kilocalories); many other countries add kilojoules. 2,000 kcal is 8,368 kJ.
What is the difference between a calorie and a Calorie?
A small calorie (cal) is 4.184 J. A food Calorie, written with a capital C or as kcal, is 1,000 of them: 4,184 J. This tool lists them as "cal" and "kcal".
How many joules are in a kilowatt-hour?
Exactly 3,600,000 J, or 3.6 MJ. It is the energy of 1,000 watts running for one hour, and the unit on electricity bills.
How many BTU are in a kWh?
About 3,412.14 BTU, using the International Table BTU of 1,055.05585262 J. Other BTU definitions differ slightly, by about 0.1%.
Is energy the same as power?
No. Power is energy per unit time: one watt is one joule per second. kWh measures energy used, kW measures the rate of use.