Quick Answer: Kilowatt-hours to Megajoules
One kilowatt-hour equals 3.6 megajoules (1 kWh = 3.6 MJ).
Conversely, 1 MJ ≈ 0.2778 kWh.
Formula: MJ = kWh × 3.6
Worked examples
- 1 kWh = 3.6 MJ
- 2 kWh = 7.2 MJ
- 5 kWh = 18 MJ
Method and limitations
One kilowatt-hour is one kilowatt sustained for 3,600 seconds. Since a watt is a joule per second, 1 kWh = 1,000 × 3,600 = 3,600,000 joules = 3.6 megajoules exactly. Calculations use full-precision constants; answers in this box are rounded for readability (≈ marks a rounded value) and the calculator shows up to 9 significant figures.
Each factor is exact by definition, derived from exact definitions, or a documented conventional value — see the methodology and sources.
Conversion Formula
One kilowatt-hour is one kilowatt sustained for 3,600 seconds. Since a watt is a joule per second, 1 kWh = 1,000 × 3,600 = 3,600,000 joules = 3.6 megajoules exactly.
Complete Guide to Kilowatt-hours to Megajoules Conversion
What is a kilowatt-hour?
A kilowatt-hour (kWh) is the amount of energy delivered by one kilowatt of power sustained for one hour. It is the billing unit for electricity almost everywhere in the world and the standard way to express battery capacity, solar production and household consumption.
What is a megajoule?
A megajoule (MJ) is one million joules; the joule is the SI unit of energy. MJ appears on some gas bills (Australian retailers are a common example), in fuel energy-content data, on gas-appliance ratings given in MJ/h, and throughout scientific work.
How the Conversion Works
The conversion rests on the definition of the watt as one joule per second. One kilowatt is 1,000 joules per second; run it for one hour (3,600 seconds) and you have delivered 3,600,000 joules, which is 3.6 MJ. Because both units are SI-derived, the factor is exact.
Why This Conversion Matters
Gas may be stated in MJ while electricity is billed in kWh. Putting both in kWh is the first step in comparing them. It is only the first step: a kWh of fuel is not a kWh of heat in the room, so a heating comparison also needs each appliance's efficiency (boiler) or seasonal performance (heat pump SCOP).
Scientific Context
The joule is defined as the work done when a force of one newton moves an object one metre. The kilowatt-hour is not an SI unit; it is built from the watt and the hour and is the usual unit for electricity metering. Because both are defined from the joule and the second, the 3.6 factor carries no measurement uncertainty.
Step-by-Step Conversion Guide
Follow these steps to convert kilowatt-hours to megajoules manually:
Start with your value in kilowatt-hours
Example: You want to convert 5 kWh
Apply the conversion formula
Use the formula: MJ = kWh × 3.6
Calculate the result
5 kWh = 18 MJ
Verify your answer
Use our calculator above to double-check your manual calculation.
Quick Mental Math Tip
One kilowatt-hour is one kilowatt sustained for 3,600 seconds. Since a watt is a joule per second, 1 kWh = 1,000 × 3,600 = 3,600,000 joules = 3.6 megajoules exactly.
Common Conversions
| Kilowatt-hours (kWh) | Megajoules (MJ) | Megajoules → Kilowatt-hours |
|---|---|---|
| 1 kWh | 3.6 | 1 MJ = 0.277778 kWh |
| 2 kWh | 7.2 | 2 MJ = 0.555556 kWh |
| 5 kWh | 18 | 5 MJ = 1.38889 kWh |
| 10 kWh | 36 | 10 MJ = 2.77778 kWh |
| 25 kWh | 90 | 25 MJ = 6.94444 kWh |
| 50 kWh | 180 | 50 MJ = 13.8889 kWh |
| 77 kWh | 277.2 | 77 MJ = 21.3889 kWh |
| 100 kWh | 360 | 100 MJ = 27.7778 kWh |
| 250 kWh | 900 | 250 MJ = 69.4444 kWh |
| 500 kWh | 1,800 | 500 MJ = 138.889 kWh |
| 1000 kWh | 3,600 | 1000 MJ = 277.778 kWh |
When You'll Need This Conversion
Comparing gas and electricity bills
Gas tariffs in MJ and electricity tariffs in kWh cannot be compared until both are expressed in the same unit.
Technical datasheets
Some datasheets and fuel data state energy in MJ, while the electricity meter reads kWh.
Physics and energy coursework
Converting between the practical unit (kWh) and the SI unit (J) is a standard exercise in energy calculations.
Gas appliance ratings
A rating in MJ/h is a power, not an energy: divide by 3.6 to express it in kW.
Pro Tips for Accurate Conversions
MJ/h ÷ 3.6 = kW
Illustrative: a 24 MJ/h gas burner rating is 24 ÷ 3.6 = 6.67 kW of fuel input.
Compare the cost of heat, not of fuel
Cost of a kWh of heat from gas = gas price per kWh ÷ boiler efficiency; from a heat pump = electricity price per kWh ÷ SCOP. Convert any MJ price to a per-kWh price first (price per MJ × 3.6).
Common Mistakes to Avoid
Confusing kW with kWh
A kilowatt is a rate of energy flow; a kilowatt-hour is a quantity of energy. A 2 kW heater running for 30 minutes uses 1 kWh.
Power (kW) × time (h) = energy (kWh). Only kWh converts to MJ.
Comparing gas MJ directly against electric kWh prices
A megajoule is far smaller than a kilowatt-hour, so gas always looks artificially cheap per unit.
Convert MJ to kWh first (÷ 3.6), then compare unit prices.
Ignoring appliance efficiency
Illustrative: a boiler at 90% efficiency delivers 0.9 kWh of heat per kWh of gas, while a heat pump with an SCOP of 3 delivers about 3 kWh of heat per kWh of electricity over a season.
Convert to delivered heat (fuel energy × efficiency, or electricity × SCOP), then compare.
History & Background
The joule is named after James Prescott Joule, whose 1840s experiments linked mechanical work and heat.
Key Milestones
Joule demonstrates the mechanical equivalent of heat, linking work and energy.
The 9th CGPM adopts the joule as the SI unit of energy, heat and work.
SI base units are redefined from physical constants, fixing the joule via the Planck constant.
Global Usage Today
Electricity is billed in kWh in most countries. MJ is used on some gas bills, for fuel energy content and in scientific publishing.
Frequently Asked Questions
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Conversion factors on this page are either exact by definition, derived from exact definitions, or conventional values in documented use. Each is listed with its source in our conversion methodology and sources, which cites the BIPM SI Brochure, NIST Special Publication 811 and the relevant IEC or national standards. Results are rounded for display only; calculations use full precision.