What is kilowatt hour?
A kilowatt hour is a unit of energy equal to 1,000 watt hours. It is the standard billing unit used by electricity providers worldwide to measure household and commercial energy consumption.
Real-world uses
The kilowatt-hour is the standard unit for electricity billing worldwide. A typical household uses 250–1,000 kWh per month. EV charging, home appliance energy consumption, and solar panel production are all expressed in kWh. Utility bills list total kWh consumed and price per kWh.
History
The kilowatt-hour became the standard billing unit for electricity in the early 20th century as public electricity grids were established. Its use is mandated for utility metering in most countries. It equals exactly 3,600,000 joules (3.6 MJ).
Common mistakes
Writing "kW/h" instead of "kWh"—the slash implies division (kW per hour), which is a rate of power change, not an energy unit. Also confusing kWh with kW: a 2 kW heater running for 4 hours uses 8 kWh of energy, not 8 kW.
What is megajoule?
A megajoule is a unit of energy equal to one million joules. It is used in industrial energy calculations, explosive yield estimations, and large-scale thermodynamic systems.
Real-world uses
Megajoules are used in energy analysis for fuel content (1 litre of petrol contains about 34.2 MJ), building energy ratings, and industrial process energy requirements. Life cycle assessment (LCA) studies report embodied energy in MJ per unit of material.
History
The megajoule became a standard unit in energy engineering and policy analysis during the 20th century. It provides a convenient scale for comparing fuel energy content, industrial processes, and building energy performance across different energy sources.
Common mistakes
Confusing MJ with MWh—1 MWh = 3,600 MJ. Also, when comparing fuel energy densities, failing to distinguish between lower heating value (LHV) and higher heating value (HHV), which can differ by 5–10% for hydrocarbon fuels.
When is this conversion used?
Electricity bills use kilowatt-hours while physics calculations use joules. Converting between them is essential for energy audits, comparing appliance efficiency, and understanding power consumption.
Worked examples
1 kilowatt hour = 3.6 megajoule
1 megajoule = 1,000,000 joule
How to convert kilowatt hour to megajoule
To convert kilowatt hour to megajoule, multiply the value by 3.6.
To convert megajoule back to kilowatt hour, multiply by 0.27777778.
Measurement standards
The joule is the SI derived unit of energy, defined as one kilogram-metre-squared per second-squared (kg·m²/s²). The kilowatt-hour, equal to exactly 3.6 megajoules, is accepted for use with the SI by the BIPM for practical electricity metering.
Did you know?
A single bolt of lightning releases roughly 1 to 5 gigajoules of energy, yet only a small fraction reaches the ground as electrical current. Most of the energy dissipates as light, heat, and the thunder shockwave.
Quick reference: kilowatt hour to megajoule
| kilowatt hour | megajoule |
|---|---|
| 0.1 | 0.36 |
| 0.5 | 1.8 |
| 1 | 3.6 |
| 2 | 7.2 |
| 5 | 18 |
| 10 | 36 |
| 25 | 90 |
| 50 | 180 |
| 100 | 360 |
| 250 | 900 |
| 500 | 1,800 |
| 1,000 | 3,600 |
Common values
| kilowatt hour | megajoule | |
|---|---|---|
| A food calorie (1 kcal) | 0.00116222 kilowatt hour | 0.004184 megajoule |
| A AA battery | 0.0026 kilowatt hour | 0.00936 megajoule |
| Boiling a kettle | 0.11666667 kilowatt hour | 0.42 megajoule |
| Daily human diet (2000 kcal) | 2.32444444 kilowatt hour | 8.368 megajoule |
| 1 gallon of gasoline | 36.6 kilowatt hour | 131.76 megajoule |
Available Energy units
More kilowatt hour conversions
- Convert kilowatt hour to joule
- Convert kilowatt hour to kilojoule
- Convert kilowatt hour to calorie (thermochemical)
- Convert kilowatt hour to kilocalorie (dietary)
- Convert kilowatt hour to watt hour
- Convert kilowatt hour to megajoule
- Convert kilowatt hour to electronvolt
- Convert kilowatt hour to British thermal unit
- Convert kilowatt hour to therm (US)
Assumption: calorie means thermochemical calorie, and therm means US therm.