Quick answer
1 kWh = 3,600,000 J = 3.6 MJ ≈ 3,412 BTU ≈ 860 kcal. To convert joules to kWh, divide by 3,600,000.
How to use the kWh to Joules Energy Converter
- Enter a number.
- Choose the unit it's in, for example kilowatt-hours (kWh).
- Read the converted values in every other unit in the table. Click a row to copy the value.
Example
Your electricity bill shows 300 kWh for a month. In joules that's 300 × 3,600,000 = 1.08 × 10⁹ J, or 1,080 MJ, about the same energy as 258,000 food kilocalories.
A gas boiler rated in BTU per hour can be compared with an electric heater by converting: 10,000 BTU ≈ 2.93 kWh.
How it works
The joule (J) is the SI unit of energy. Every other unit is a fixed multiple of it:
| Unit | In joules |
|---|---|
| 1 watt-hour (Wh) | 3,600 J |
| 1 kilowatt-hour (kWh) | 3,600,000 J = 3.6 MJ |
| 1 calorie (cal, thermochemical) | 4.184 J |
| 1 kilocalorie (kcal, food Calorie) | 4,184 J |
| 1 British thermal unit (BTU, IT) | 1,055.06 J |
| 1 therm (US) | 105,480,400 J |
| 1 foot-pound force (ft·lbf) | 1.3558 J |
| 1 electronvolt (eV) | 1.602 × 10⁻¹⁹ J |
A watt is one joule per second, so a 1,000 W device running for one hour uses 3.6 million joules, which is 1 kWh.
Make sense of energy numbers
- Electricity cost: multiply kWh by your price per kWh. A 2,000 W heater running 3 hours uses 6 kWh; at €0.35/kWh that's €2.10.
- Food vs. electricity: a 2,000 kcal daily diet is about 2.3 kWh, roughly the energy a 2,000 W kettle uses in 70 minutes.
- Car fuel: one liter of petrol holds about 8.9 kWh (32 MJ) of chemical energy.
- Air conditioners: BTU/h is a power rating. A 12,000 BTU/h air conditioner moves about 3.5 kW of heat.
- Batteries: a 1 kWh home battery could, in theory, power a 100 W device for 10 hours before losses.
Frequently asked questions
How many joules are in a kWh?
Exactly 3,600,000 joules (3.6 MJ). A kilowatt is 1,000 joules per second, and an hour has 3,600 seconds.
How do I convert joules to kWh?
Divide by 3,600,000. For example, 7,200,000 J ÷ 3,600,000 = 2 kWh.
Is a food Calorie the same as a calorie?
No. A food Calorie (capital C) is a kilocalorie, 1,000 calories or 4,184 J.
How many BTU is 1 kWh?
About 3,412 BTU. This is often used to compare air conditioners and heaters.
What's the difference between kW and kWh?
kW is power, the rate of using energy. kWh is energy, power multiplied by time. A 2 kW heater running for 3 hours uses 6 kWh.