Convert electrical or thermal power into gigajoules for gas bills, district heating and energy audits.
Need the power figure before the energy figure? Work it out with the kVA to kW converter first.
Every diagram and table on this page updates with the calculator above.
One kilowatt-hour is 3.6 megajoules, which is 0.0036 gigajoules.
A 500 kW boiler running for 10 hours delivers 18 GJ of heat, which is the same as 5,000 kWh.
Natural gas is billed per GJ across most Canadian provinces.
Heat networks across Europe meter delivered heat in GJ or MWh.
Steam and process heat balances are routinely kept in GJ.
Many national inventories express fuel energy in GJ or TJ.
The split is essentially historical: electricity grew up with the kilowatt-hour, while fuels and heat inherited the joule from thermodynamics.
Gigajoules add up quickly on heating plant. The area below is the energy delivered at your power level for the hours selected — adjust either slider to see how output and run time trade off.
Your power level converted across common run times.
| h | Energy (GJ) | Energy (kWh) |
|---|---|---|
| 1 h | 1.8 | 500 |
| 2 h | 3.6 | 1,000 |
| 4 h | 7.2 | 2,000 |
| 8 h | 14.4 | 4,000 |
| 12 h | 21.6 | 6,000 |
| 24 h | 43.2 | 12,000 |
| 48 h | 86.4 | 24,000 |
| 168 h | 302.4 | 84,000 |
| 336 h | 604.8 | 168,000 |
| 730 h | 1,314 | 365,000 |
| 2,190 h | 3,942 | 1,095,000 |
| 8,760 h | 15,768 | 4,380,000 |
Comparing heating options honestly means putting gas, electricity and heat network prices into the same unit — and then correcting for efficiency, which is where most comparisons fall down.
Divide any price per GJ by 277.8 to get the equivalent price per kWh.
A 90% efficient boiler delivers 0.9 kWh of heat per kWh of gas. A heat pump with a COP of 3 delivers 3 kWh of heat per kWh of electricity.
Only after both corrections are the numbers genuinely comparable.
Almost identical cost per unit of delivered heat — the raw tariffs suggested a threefold difference.
29 calculators built on the same maths as the tool above. Each one has its own inputs, interactive diagrams and worked examples.
Common questions about converting kw to gj.