How to use the Energy Converter
- Enter the amount of energy.
- Choose the unit you have.
- Choose the unit you want.
- Read the result, the rate and the reference table.
Formula used
Result = Value × (joules per source unit ÷ joules per target unit). 1 cal = 4.184 J, 1 kcal = 4,184 J, 1 Wh = 3,600 J, 1 kWh = 3,600,000 J, 1 BTU = 1,055.056 J.
Worked example
Here is the Energy Converter worked through with the example values shown above, so you can check each step by hand.
| Inputs | |
|---|---|
| Value | 1 |
| From | Kilowatt-hours (kWh) |
| To | Kilojoules (kJ) |
| Result | |
| Converted value | 3,600 |
| Conversion rate | 1 kWh = 3,600 kJ |
Quick reference table
Common values converted with the units selected above.
| From | To |
|---|---|
| 1 kWh | 3,600 kJ |
| 10 kWh | 36,000 kJ |
| 100 kWh | 360,000 kJ |
| 500 kWh | 1,800,000 kJ |
| 1,000 kWh | 3,600,000 kJ |
| 2,000 kWh | 7,200,000 kJ |
Key relationships
The joule is the SI unit. One kilojoule is 1,000 J. A watt-hour is 3,600 J because one watt for one hour is 1 J per second for 3,600 seconds, and a kilowatt-hour is 3,600 kJ.
Calories need care. A small calorie is 4.184 J, and a food Calorie (kcal, written with a capital C on labels) is 1,000 of them, 4.184 kJ. So a 250 kcal snack carries 1,046 kJ, the figure European labels print.
Electricity and food
One kWh is the energy a 1,000 watt appliance uses in an hour, and it equals 860.42065 kcal. A 2,000 kcal day of eating is 2.324444 kWh, about what a small appliance uses running for a few hours.
This comparison only converts units. The body is not a heater, and food energy and electrical energy are not interchangeable in practice, but the numbers help put each in perspective.
Heating and cooling
One BTU is 1,055.055853 J. A 12,000 BTU per hour air conditioner, often called a one-ton unit, removes about 3.516853 kWh of heat each hour. Use the power converter for BTU per hour and watts.
Gas bills in some countries use therms or cubic metres, which depend on the gas energy content and are not covered here.
Energy versus power
Energy is an amount (kWh, J). Power is a rate of using it (kW, W). A 3 kW heater running for 2 hours uses 6 kWh. If you mix them up, conversions will not make sense: you cannot convert kW to kWh without a time.
The power converter on this site handles watts, kilowatts and horsepower.
Putting the numbers in context
A typical mobile phone battery holds about 15 Wh, which is 54 kJ. A litre of petrol contains roughly 34 MJ of energy, about 9.4 kWh, which is why fuel is such a compact store compared with batteries.
A person at rest uses about 80 to 100 watts, so about 2 to 2.4 kWh a day, consistent with the 1,700 to 2,000 kcal many adults need. These are rough everyday figures meant to give scale, not precise data.
Frequently asked questions
How many joules are in a kWh?
Exactly 3,600,000 joules, or 3,600 kilojoules.
Is a food Calorie the same as a kilocalorie?
Yes. The Calories on a label are kilocalories, equal to 4,184 joules.
How many kcal are in a kWh?
About 860.42065 kcal.
What is a BTU?
A British thermal unit, the heat needed to raise a pound of water by one degree Fahrenheit. It is about 1,055.055853 joules.
Can I convert kW to kWh?
Only with a time. Energy in kWh = power in kW × hours.
Which calorie does this use?
The thermochemical calorie of 4.184 joules, the most common definition. Other calorie definitions differ by a fraction of a percent.
This calculator gives estimates for information only. Actual figures from a bank, employer, tax authority or doctor may differ. It is not financial, tax, legal or medical advice.