kWh to MJ — the exact energy conversion
This converter turns kilowatt-hours (kWh), the unit on your electricity bill, into megajoules (MJ), the SI unit of energy, and back again. It is useful for comparing electricity use against gas energy content, sizing batteries, or checking engineering figures that mix the two units.
How it works
The factor is exact: a watt is one joule per second, so
1 kWh = 1000 W × 3600 s = 3,600,000 J = 3.6 MJ.
To convert kilowatt-hours to megajoules the tool multiplies by 3.6; to convert megajoules back to kilowatt-hours it divides by 3.6. You pick the direction and the result updates instantly.
Worked examples
Example 1 — household electricity to MJ: A household uses 12 kWh of electricity in a day. In megajoules:
12 × 3.6 = 43.2 MJ
Example 2 — gas calorific value to kWh: A gas supplier quotes the energy content of a delivery as 540 MJ. To find the equivalent in kilowatt-hours:
540 ÷ 3.6 = 150 kWh
This lets you add it to your electricity figure for a combined household energy total.
Example 3 — battery sizing: A battery specification lists capacity as 7.2 MJ. In kWh:
7.2 ÷ 3.6 = 2 kWh
That maps directly to what you would see on a domestic battery product label.
When you need this conversion
| Situation | Direction |
|---|---|
| Comparing electricity bill (kWh) with gas bill (MJ) | kWh → MJ |
| Converting a science or engineering spec listed in MJ | MJ → kWh |
| Sizing a home battery bank against daily usage in kWh | kWh → MJ or MJ → kWh |
| Checking fuel calorific values quoted in MJ/litre | MJ → kWh |
The two units appear together most often when you are doing a whole-home energy audit — electricity meters report in kWh, but gas and LPG energy content is frequently quoted in MJ or GJ in government and engineering documents. Dividing by 3.6 (or multiplying, depending on direction) is all that is needed.
Practical tips
- Precision: The factor 3.6 is exact by definition — not a rounded approximation — so there is no rounding error in the conversion itself. Any imprecision comes from your input figure.
- Large quantities: For very large values (gigajoules or megawatt-hours), remember that 1 GJ = 1,000 MJ = 277.78 kWh, and 1 MWh = 1,000 kWh = 3,600 MJ. Scale accordingly.
- Gas meter readings: Gas meters often display in cubic metres (m³). Your gas supplier converts that volume to an energy figure (MJ or kWh) using the calorific value of the gas. The conversion here is for energy units only, not volume-to-energy.
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