About this calculator
Type a number, choose the unit you have and the unit you want, and this converter gives you the answer at once, along with the same energy and heat in every other unit it knows.
Every conversion factor is exact by definition wherever one exists, and each result shows the working so you can check it.
Worked examples
Real numbers, worked out by the same calculator. Press “Use these numbers” to try one above.
1 kWh to kJ
- kilojoules (kJ)
- 3,600 kJ
- joules (J)
- 3,600,000 J
- calories (cal)
- 860,420.650096 cal
- kilocalories (kcal)
- 860.420650096 kcal
- watt-hours (Wh)
- 1,000 Wh
- British thermal units (BTU)
- 3,412.14163313 BTU
- foot-pounds (ft·lbf)
- 2,655,223.7374 ft·lbf
- electronvolts (eV)
- 2.24694327e+25 eV
1 kWh is 3,600 kJ.
Show the working
- Change to the base unit (J): 1 kWh × 3,600,000 = 3,600,000 J.
- Change to kJ: 3,600,000 ÷ 1,000 = 3,600 kJ.
2,000 kcal to kJ
- kilojoules (kJ)
- 8,368 kJ
- joules (J)
- 8,368,000 J
- calories (cal)
- 2,000,000 cal
- watt-hours (Wh)
- 2,324.44444444 Wh
- kilowatt-hours (kWh)
- 2.32444444444 kWh
- British thermal units (BTU)
- 7,931.33366278 BTU
- foot-pounds (ft·lbf)
- 6,171,920.06515 ft·lbf
- electronvolts (eV)
- 5.22289479e+25 eV
2,000 kcal is 8,368 kJ.
Show the working
- Change to the base unit (J): 2,000 kcal × 4,184 = 8,368,000 J.
- Change to kJ: 8,368,000 ÷ 1,000 = 8,368 kJ.
1 BTU to J
- joules (J)
- 1,055.05585262 J
- kilojoules (kJ)
- 1.05505585262 kJ
- calories (cal)
- 252.164400722 cal
- kilocalories (kcal)
- 0.252164400722 kcal
- watt-hours (Wh)
- 0.293071070172 Wh
- kilowatt-hours (kWh)
- 0.00029307107017 kWh
- foot-pounds (ft·lbf)
- 778.169262266 ft·lbf
- electronvolts (eV)
- 6.58514068e+21 eV
1 BTU is 1,055.05585262 J.
Show the working
- Change to the base unit (J): 1 BTU × 1,055.05585262 = 1,055.05585262 J.
- Change to J: 1,055.05585262 ÷ 1 = 1,055.05585262 J.
How to convert by hand
Every energy unit is stored in joules. Multiply by the size of the unit you have (in J), then divide by the size of the unit you want. For example, 2 kWh × 3,600,000 = 7,200,000 J (7.2 MJ).
One watt-hour is one watt for one hour, so 3,600 joules; a kilowatt-hour is 3.6 million joules.
Conversion factors used
Each unit is stored as its size in J. The sizes below are the ones this converter uses.
| Unit | Size |
|---|---|
| joules (J) | 1 J |
| kilojoules (kJ) | 1,000 J |
| calories (cal) | 4.184 J |
| kilocalories (kcal) | 4,184 J |
| watt-hours (Wh) | 3,600 J |
| kilowatt-hours (kWh) | 3,600,000 J |
| British thermal units (BTU) | 1,055.05585262 J |
| foot-pounds (ft·lbf) | 1.35581794833 J |
| electronvolts (eV) | 1.60217663e-19 J |
Common conversions
| From | To |
|---|---|
| 1 kcal | 4.184 kJ |
| 1 kWh | 3,600 kJ |
| 1 kWh | 860.420650096 kcal |
| 1 kWh | 3,412.14163313 BTU |
| 100 kcal | 418.4 kJ |
| 1 BTU | 1,055.05585262 J |
| 1 Wh | 3,600 J |
| 1 ft·lbf | 1.35581794833 J |
Food calories
The “Calories” on food labels are really kilocalories (kcal): 1 kcal is 4,184 joules. That is why a 2,000 kcal day is about 8,368 kJ, the figure labels show next to it. The calorie here is the thermochemical calorie (4.184 J).
Frequently asked questions
How many kJ is one kcal?
One kilocalorie is 4.184 kilojoules.
How many joules are in a kWh?
One kilowatt-hour is 3,600,000 joules (3.6 MJ).
What is a BTU?
A British thermal unit is about 1,055 joules, roughly the energy to warm a pound of water by one degree Fahrenheit.
How accurate is this converter?
It uses the exact defined factors wherever they exist and shows up to 12 significant digits, so the results are accurate to far more digits than you will normally need.
Formulas tested against hand-worked answers. Last reviewed 29 September 2026. These calculators do arithmetic only; they are not financial, tax or legal advice.