Convert megajoules to kWh, kWh to MJ, or estimate electricity cost from MJ energy using a per-kWh rate in USD, EUR, GBP, CAD, or AUD.
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Megajoules to kWh Formula
kWh = MJ ÷ 3.6
MJ = kWh × 3.6
Cost = (MJ ÷ 3.6) × price per kWh
- MJ = energy in megajoules (1 MJ = 1,000,000 joules)
- kWh = energy in kilowatt-hours (1 kWh = 3,600,000 joules)
- price per kWh = your electricity rate in your local currency
The conversion factor 3.6 comes from the definition: 1 kWh equals 3,600 seconds × 1,000 W = 3,600,000 J = 3.6 MJ. The relationship is exact, not an approximation.
Quick Reference Tables
Common conversions in both directions:
| Megajoules (MJ) | Kilowatt-hours (kWh) |
|---|---|
| 1 MJ | 0.2778 kWh |
| 3.6 MJ | 1 kWh |
| 10 MJ | 2.7778 kWh |
| 36 MJ | 10 kWh |
| 100 MJ | 27.778 kWh |
| 1,000 MJ (1 GJ) | 277.78 kWh |
Typical energy figures for context:
| Item | MJ | kWh |
|---|---|---|
| Boiling 1 L of water | ~0.34 | ~0.094 |
| Running a 1,500 W heater for 1 hr | 5.4 | 1.5 |
| Average daily home use (US) | ~108 | ~30 |
| 1 m³ natural gas (heat content) | ~38 | ~10.6 |
| 1 L gasoline (heat content) | ~34 | ~9.4 |
Worked Examples
Convert 50 MJ to kWh: 50 ÷ 3.6 = 13.889 kWh.
Convert 25 kWh to MJ: 25 × 3.6 = 90 MJ.
Cost of 180 MJ at $0.16/kWh: 180 ÷ 3.6 = 50 kWh, then 50 × 0.16 = $8.00.
Why 3.6? A kilowatt-hour is 1,000 watts sustained for one hour (3,600 seconds). That equals 3,600,000 joules, or 3.6 MJ. So dividing MJ by 3.6 gives kWh every time.
Note on gas bills: Utility bills sometimes list gas in MJ and electricity in kWh. The conversion above gives the energy equivalence, but it does not account for appliance efficiency. A gas heater and electric heater rated for the same kWh output will use different amounts of input energy.