Units
Energy converter
Kilowatt-hours to joules, calories to kilojoules, BTU to kJ. For electricity bills, food labels and air conditioning.
Conversions are worked out on your own machine. No sign-up, no waiting and nothing sent anywhere.
Common conversions
| kilowatt-hour | megajoule |
|---|---|
| 1 kWh | 3.6 MJ |
| 2 kWh | 7.2 MJ |
| 5 kWh | 18 MJ |
| 10 kWh | 36 MJ |
| 50 kWh | 180 MJ |
| 100 kWh | 360 MJ |
| 1,000 kWh | 3,600 MJ |
| kilocalorie | kilojoule |
|---|---|
| 1 kcal | 4.184 kJ |
| 2 kcal | 8.368 kJ |
| 5 kcal | 20.92 kJ |
| 10 kcal | 41.84 kJ |
| 50 kcal | 209.2 kJ |
| 100 kcal | 418.4 kJ |
| 1,000 kcal | 4,184 kJ |
| British thermal unit | kilojoule |
|---|---|
| 1 BTU | 1.0551 kJ |
| 2 BTU | 2.1101 kJ |
| 5 BTU | 5.2753 kJ |
| 10 BTU | 10.551 kJ |
| 50 BTU | 52.753 kJ |
| 100 BTU | 105.506 kJ |
| 1,000 BTU | 1,055.06 kJ |
| joule | calorie |
|---|---|
| 1 J | 0.239006 cal |
| 2 J | 0.478011 cal |
| 5 J | 1.195 cal |
| 10 J | 2.3901 cal |
| 50 J | 11.95 cal |
| 100 J | 23.901 cal |
| 1,000 J | 239.006 cal |
| kilowatt-hour | British thermal unit |
|---|---|
| 1 kWh | 3,412.14 BTU |
| 2 kWh | 6,824.28 BTU |
| 5 kWh | 17,060.71 BTU |
| 10 kWh | 34,121.42 BTU |
| 50 kWh | 170,607.08 BTU |
| 100 kWh | 341,214.16 BTU |
| 1,000 kWh | 3,412,141.63 BTU |
Worked out with the same factors the converter above uses.
The SI unit is the joule, but in practice every sector uses its own. The electricity bill talks in kilowatt-hours, which are 3.6 million joules: what a 1,000-watt appliance uses running for an hour. Food labels talk in kilocalories, and American air conditioning in BTU.
The calorie carries a confusion worth clearing up: the “calorie” on food labels is really a kilocalorie, a thousand times bigger than the physicist's calorie. An “80 calorie” apple holds 80 kcal, or 334.7 kilojoules. That is why European labels carry both figures, kJ and kcal, with the first about 4.2 times the second.
The BTU (British thermal unit) is the energy to raise one pound of water by one degree Fahrenheit, and air conditioning uses its per-hour version to state cooling power. A “12,000 BTU” unit is about 3.5 kW: if you have ever compared units between European and American catalogues, this is the conversion you needed.
Every unit in this category
Frequently asked questions
How many joules are in a kilowatt-hour?
3,600,000 joules, or 3.6 megajoules. That is 1,000 watts for 3,600 seconds.
Are food calories the same as physics calories?
No: food calories are kilocalories, a thousand times larger. When a label says “250 calories” it means 250 kcal, which is 1,046 kilojoules.
How many watts is a 12,000 BTU air conditioner?
About 3,517 watts, or 3.5 kW. The BTU figure in catalogues is really BTU per hour — a power, not an energy.