Energy Converter
Convert joules, calories, kWh, BTU, and more. Free instant energy unit converter.
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All units
| Unit | Value | Copy |
|---|---|---|
| JouleJ | 418400 | |
| KilojoulekJ | 418.4 | |
| Caloriecal | 100000 | |
| Kilocaloriekcal | 100 | |
| Watt-hourWh | 116.22222 | |
| Kilowatt-hourkWh | 0.11622222 | |
| BTUBTU | 396.56668 | |
| Foot-poundft·lb | 308596 | |
| ElectronvolteV | 2.611447e+24 |
Popular conversions
How energy conversion works
All energy units here are stored in joules, the SI unit. A watt-hour is one watt for one hour, 3,600 J, so a kilowatt-hour is 3.6 million joules. The calorie used in nutrition is the kilocalorie (kcal, written Calorie with a capital C on US labels), defined here as 4,184 J. The British thermal unit (BTU, International Table) is about 1,055.06 J.
To convert, the tool multiplies by the source unit's size in joules and divides by the target's. Power is a different quantity (energy per second); use the power converter for watts, horsepower and BTU per hour.
Worked examples
Food labels, kcal to kJ
A 2,000 kcal daily diet is 2,000 × 4.184 = 8,368 kJ. In the other direction, an 840 kJ snack is 840 ÷ 4.184 = 200.8 kcal.
Electricity bills, appliance use to kWh
A 1,500 W heater running for 3 hours uses 1.5 kW × 3 h = 4.5 kWh, which is 16.2 million joules. Multiply by your price per kWh to get the cost.
Heating and cooling, BTU to kWh
100,000 BTU is 100,000 × 1,055.06 ÷ 3,600,000 = 29.31 kWh. One kWh is about 3,412 BTU.
Energy amounts in common units
| kWh | J | kcal | BTU | |
|---|---|---|---|---|
| 1 watt-hour | 0.001 | 3,600 | 0.860421 | 3.41214 |
| Phone charge (example, about 15 Wh) | 0.015 | 54,000 | 12.9063 | 51.1821 |
| 1 kilowatt-hour | 1 | 3,600,000 | 860.421 | 3,412.14 |
| 1,500 W heater for 3 hours | 4.5 | 16,200,000 | 3,871.89 | 15,354.6 |
| Daily diet of 2,000 kcal | 2.32444 | 8,368,000 | 2,000 | 7,931.33 |
Common mistakes
- Confusing kW and kWh. kW is a rate (power); kWh is an amount (energy). A 2 kW kettle used for 6 minutes uses 0.2 kWh.
- Mixing small calories and food Calories. 1 food Calorie = 1 kcal = 1,000 cal. A 250 Calorie bar is 250 kcal, about 1,046 kJ.
- Using BTU when the figure is BTU per hour. Air conditioner ratings like 12,000 BTU are really BTU/h, a power. Convert those on the power page.
- Expecting every calorie to equal 4.184 J. That is the thermochemical calorie; the International Table calorie is 4.1868 J (NIST SP 811). The difference is under 0.1%.
Sources
Frequently asked questions
How many joules in a kilocalorie?
1 kcal equals 4,184 joules.
How many joules in a kWh?
1 kWh equals 3,600,000 joules.
How many joules in a BTU?
1 BTU (International Table) is about 1,055.06 joules, and 1 kWh is about 3,412 BTU.
Is a food Calorie the same as a calorie?
No. A food Calorie (capital C) is a kilocalorie: 1 Cal = 1 kcal = 1,000 small calories ≈ 4,184 joules.
How many kcal are in a kWh?
About 860.4 kcal, since 3,600,000 J ÷ 4,184 J = 860.4.
How do I work out kWh from watts?
Multiply watts by hours and divide by 1,000. A 60 W bulb for 5 hours uses 0.3 kWh.