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Convert Energy: Watt-hour (Wh), Kilowatt-hour (kWh), Megawatt-hour (MWh), Joule (J) and Calorie
This converter lets you quickly convert energy units: watt-hour (Wh), kilowatt-hour (kWh), megawatt-hour (MWh), gigawatt-hour (GWh), terawatt-hour (TWh), as well as joules (J, kJ, MJ, GJ), calories (cal, kcal), BTU and the tonne of oil equivalent (toe).
What is a kilowatt-hour (kWh)?
The kilowatt-hour is the unit used every day to measure electrical energy: it is the energy consumed by a 1-kilowatt (kW) device running for 1 hour. It is the unit that appears on your electricity or gas bill. In the International System, the official unit of energy is the joule (J): 1 kWh = 3,600,000 J, i.e. 3.6 megajoules (MJ).
How to use the converter?
Select the source unit in the first drop-down list, type the value to convert, then choose the target unit in the second list. The result is displayed automatically. The ↑↓ button swaps the two units in a single click.
kWh, MWh, GWh, TWh: the orders of magnitude of electricity
The multiples of the watt-hour follow the decimal system: each step is 1,000 times the previous one.
- The kilowatt-hour (kWh) = 1,000 Wh: the household scale. An average American home consumes about 10,500 kWh of electricity per year.
- The megawatt-hour (MWh) = 1,000 kWh: the scale of industry and electricity markets, where prices are quoted in $/MWh.
- The gigawatt-hour (GWh) = 1,000 MWh: the scale of a city or a power plant.
- The terawatt-hour (TWh) = 1,000 GWh: the scale of a country. The United States consumes about 4,000 TWh of electricity per year.
Energy unit conversion table
| Unit | Value in joules |
|---|---|
| 1 watt-hour (Wh) | 3,600 J |
| 1 kilowatt-hour (kWh) | 3,600,000 J |
| 1 megawatt-hour (MWh) | 3,600,000,000 J |
| 1 gigawatt-hour (GWh) | 3,600,000,000,000 J |
| 1 calorie (cal) | 4.184 J |
| 1 kilocalorie (kcal) | 4,184 J |
| 1 BTU | ≈ 1,055.06 J |
| 1 tonne of oil equivalent (toe) | 41,868,000,000 J (11,630 kWh) |
kW and kWh: don't confuse them
Watch out for the difference between the kilowatt (kW) and the kilowatt-hour (kWh). The kW measures power (the "speed" at which energy is consumed or produced), while the kWh measures energy (a quantity). The relationship between the two involves time: energy (kWh) = power (kW) × duration (h). A 2 kW heater running for 3 hours therefore consumes 2 × 3 = 6 kWh.
Calories, BTU and tonne of oil equivalent
The calorie (1 cal = 4.184 J) is mainly used in nutrition: the "calories" on food labels are actually kilocalories (1 kcal = 4,184 J ≈ 1.162 Wh). The BTU (British Thermal Unit, ≈ 1,055.06 J) is common for air conditioners and heaters in the United States. The tonne of oil equivalent (toe) is used in energy assessments: it represents the energy released by burning one tonne of oil, i.e. 11,630 kWh.
Saving your data
You can save your conversions by clicking the Save button. The recorded results can then be exported in CSV or PDF format.
Frequently asked questions about energy conversion
How many kWh in 1 MWh?
A megawatt-hour (MWh) contains 1,000 kilowatt-hours (kWh). Likewise, 1 GWh = 1,000 MWh and 1 TWh = 1,000 GWh.
How many joules in 1 kWh?
A kilowatt-hour is exactly 3,600,000 joules, i.e. 3.6 megajoules (MJ): 1 kW = 1,000 W and 1 hour = 3,600 seconds, so 1 kWh = 1,000 × 3,600 = 3,600,000 J.
What is the difference between kW and kWh?
The kilowatt (kW) measures power, the kilowatt-hour (kWh) measures energy. A 2 kW device running for 3 hours consumes 6 kWh.
How many kWh in a tonne of oil equivalent (toe)?
A tonne of oil equivalent is 11,630 kWh, i.e. 41.868 gigajoules (GJ).
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