Where each energy unit is used
- Joule (J) and kilojoule (kJ) are the SI units. Food labels in Europe and Australia show kJ next to kcal.
- Kilocalorie (kcal) is the food Calorie with a capital C. A snack with 200 Calories has 200 kcal, or about 837 kJ.
- Kilowatt-hour (kWh) is how electricity is billed. A 1,000 W heater running for one hour uses 1 kWh.
- British thermal unit (BTU) rates heaters and air conditioners in the US. 1 kWh is about 3,412 BTU.
- Electronvolt (eV) is used in physics for the energy of single particles.
This converter uses the thermochemical calorie of exactly 4.184 joules, which is what food labels are based on. The international table calorie of 4.1868 J differs by less than 0.1 percent.
Common energy conversions
| From | Equals |
|---|---|
| 1 kilocalorie | 4.184 kilojoules |
| 1 kilojoule | 0.2390057361 kilocalories |
| 1 kilowatt-hour | 3,412.141633 British thermal units |
| 1 kilowatt-hour | 3,600,000 joules |
| 1 British thermal unit | 1.055055853 kilojoules |
| 1 watt-hour | 3,600 joules |
| 1 calorie | 4.184 joules |
Food energy: kcal to kJ
| Kilocalories (kcal) | Kilojoules (kJ) |
|---|---|
| 50 | 209.2 |
| 100 | 418.4 |
| 150 | 627.6 |
| 200 | 836.8 |
| 250 | 1,046 |
| 300 | 1,255.2 |
| 400 | 1,673.6 |
| 500 | 2,092 |
| 1,000 | 4,184 |
| 1,500 | 6,276 |
| 2,000 | 8,368 |
| 2,500 | 10,460 |
Where the conversions come up
Food labels are the main reason: European and Australian packaging lists kJ first, Americans count Calories, and a 2,000 kcal day is 8,368 kJ. Heating and cooling is the other big one. Air conditioners and gas heaters in the US are rated in BTU per hour, European ones in kW, and an electricity bill is always in kWh. Gym machines show calories burned, which is kcal, and the same workout logged in kJ looks four times more impressive.
Shortcuts: kcal to kJ is times 4.2, kJ to kcal is divide by 4.2. One kWh is about 860 kcal or 3,412 BTU. A 12,000 BTU per hour air conditioner is a 3.5 kW unit.
How to use it
- 1Pick the unit on the label or spec sheet on the left and the one you want on the right. kcal to kJ is set up when the page opens.
- 2Type the amount. Either side accepts input, and swap turns the conversion around.
- 3Read the result and see the same energy in joules, watt-hours, BTU and the rest in the list. Copy the number or a link.
Frequently asked questions
How many kJ are in a kcal?
Exactly 4.184. A daily intake of 2,000 kcal is 8,368 kJ.
What is the difference between a calorie and a Calorie?
The Calorie on food labels, with a capital C, is a kilocalorie: 1,000 small calories. Most people mean kcal when they say calories.
How many BTU are in a kWh?
About 3,412 BTU. A 12,000 BTU per hour air conditioner moves about 3.5 kW of heat.
What does 1 kWh of electricity mean?
It is the energy a 1,000 watt device uses in one hour, or 3.6 million joules.
How many calories are in a kilojoule?
0.239 kcal. Divide kJ by 4.184, so a 1,500 kJ snack is about 359 kcal.