Convert g CO₂/MJ to g CO₂/kWh
| g CO₂e/MJ | g CO₂e/kWh |
|---|---|
| 0.5 | 1.8 |
| 1 | 3.6 |
| 1.5 | 5.4 |
| 2 | 7.2 |
| 3 | 10.8 |
| 5 | 18 |
| 10 | 36 |
| 20 | 72 |
| 50 | 180 |
| 100 | 360 |
Each row uses the same factor as the converter above: 1 g CO₂e/MJ = 3.6 g CO₂e/kWh.
Energy-based emission factors come in two flavours: per megajoule (MJ), the unit of scientific and inventory work, and per kilowatt-hour (kWh), the unit of electricity meters and appliances. They differ only by the size of the energy unit: 1 kWh = 3.6 MJ, so a per-kWh figure is 3.6 times the per-MJ one. Multiply g CO₂/MJ by 3.6 to get g CO₂/kWh. It works the same for CO₂ and CO₂e.
To convert g CO₂/MJ to g CO₂/kWh, multiply by 3.6 (because 1 kWh = 3.6 MJ). So a fuel at 56 g CO₂/MJ is 56 × 3.6 ≈ 202 g CO₂/kWh. To reverse it, divide g CO₂/kWh by 3.6.
g CO₂/kWh = g CO₂/MJ × 3.6. Reverse: g CO₂/MJ = g CO₂/kWh ÷ 3.6. The 3.6 is exact — one kilowatt-hour is 3.6 megajoules (1 Wh = 3,600 J). The same factor applies to CO₂ or CO₂e, and to any per-energy intensity.
| g CO₂/MJ | × 3.6 | g CO₂/kWh |
|---|---|---|
| 56.1 (natural gas) | × 3.6 | 202 g CO₂/kWh |
| 74.1 (diesel) | × 3.6 | 267 g CO₂/kWh |
| 94.6 (hard coal) | × 3.6 | 341 g CO₂/kWh |
| 1 | × 3.6 | 3.6 g CO₂/kWh |
Why the same fuel has two numbers
A kilowatt-hour and a megajoule both measure energy — they are just different sizes. One kWh (a thousand watts for an hour) equals 3.6 MJ. So a fuel that releases a fixed amount of CO₂ per unit of energy has a per-kWh figure exactly 3.6 times its per-MJ figure. Nothing about the fuel changes; only the denominator does.
1 kWh = 3.6 MJ, 1 GJ = 277.8 kWh, 1 MWh = 3,600 MJ = 3.6 GJ. Inventory factors are often quoted per gigajoule (kg CO₂/GJ) or per terajoule (t CO₂/TJ); numerically, kg CO₂/GJ and g CO₂/MJ are the same value, so 56 kg CO₂/GJ = 56 g CO₂/MJ = 202 g CO₂/kWh.
Carbon intensity of common fuels, both ways
These are IPCC default CO₂ emission factors for fuel combustion, shown in both units. They are the numbers you convert when a factor is published per MJ (or per GJ) but you need it per kWh:
| Fuel | g CO₂/MJ (= kg/GJ) | g CO₂/kWh |
|---|---|---|
| Natural gas | 56.1 | 202 |
| LPG | 63.1 | 227 |
| Motor gasoline | 69.3 | 249 |
| Diesel / gas oil | 74.1 | 267 |
| Fuel oil | 77.4 | 279 |
| Hard coal | 94.6 | 341 |
IPCC 2006 default CO₂ factors, net calorific value basis. The EU Renewable Energy Directive uses the same unit for transport fuels — its fossil-fuel comparator is 94 gCO₂e/MJ (≈ 338 g/kWh), well-to-wheel.
Per-energy factors depend on whether the energy is measured as net (lower) or gross (higher) calorific value. A factor per MJ(net) and one per MJ(gross) for the same fuel differ by a few percent (about 10% for natural gas). The ×3.6 unit step is exact, but only compare or combine factors that share the same NCV/GCV basis — mixing them is a common, hidden error.
g CO₂/MJ to g CO₂/kWh conversion table
The table reads both ways — per MJ to per kWh on the left (× 3.6), per kWh back to per MJ on the right (÷ 3.6).
| g CO₂/MJ | → g/kWh (× 3.6) | g CO₂/kWh | → g/MJ (÷ 3.6) |
|---|---|---|---|
| 10 | 36 | 100 | 27.8 |
| 50 | 180 | 200 | 55.6 |
| 56.1 | 202 | 300 | 83.3 |
| 74.1 | 267 | 400 | 111.1 |
| 94.6 | 341 | 500 | 138.9 |
Where each unit is used
- Per MJ / GJ / TJ — inventories and science. The IPCC, IEA and national greenhouse-gas inventories publish fuel emission factors per unit of energy content, usually kg CO₂/GJ (numerically the same as g CO₂/MJ).
- Per kWh — electricity and appliances. Grid factors, meters, appliance labels and building energy models work in kWh, so an MJ-based fuel factor has to be converted before it lines up with electricity figures (see CO₂/kWh to /MWh).
- Per MJ — transport-fuel standards. The EU Renewable Energy Directive and low-carbon fuel standards express well-to-wheel carbon intensity in gCO₂e/MJ, the unit used to rank biofuels and e-fuels against the fossil comparator.
- Estimating combustion emissions. To turn fuel energy into CO₂ you multiply by the factor; the stationary combustion calculator does the full estimate, while this converter just changes the factor’s energy basis.
Frequently Asked Questions
Multiply by 3.6, because one kilowatt-hour is 3.6 megajoules. For example, 56 g CO₂/MJ × 3.6 ≈ 202 g CO₂/kWh. To reverse it, divide g CO₂/kWh by 3.6. The factor is exact and applies to CO₂ or CO₂e.
A watt is one joule per second, so a kilowatt-hour is 1,000 W × 3,600 s = 3,600,000 J = 3.6 MJ. It is an exact definition, which is why the conversion has no rounding.
Numerically, yes. A gigajoule is a thousand megajoules and a kilogram is a thousand grams, so the two thousands cancel: 56 kg CO₂/GJ = 56 g CO₂/MJ. Both equal about 202 g CO₂/kWh.
About 202 g CO₂ per kWh of fuel energy (56.1 g/MJ × 3.6), using the IPCC default factor. Diesel is around 267 g/kWh and hard coal around 341 g/kWh. These are the fuel’s own combustion CO₂, not grid electricity.
Yes. A factor per unit of net (lower) calorific value differs from one per gross (higher) calorific value by a few percent — around 10% for natural gas. The MJ-to-kWh step is exact, but only compare factors that share the same NCV or GCV basis.
Transport-fuel policies like the EU Renewable Energy Directive rank fuels by well-to-wheel carbon intensity per unit of energy delivered, and the megajoule is the SI energy unit for that. Its fossil comparator is 94 gCO₂e/MJ, or about 338 g/kWh.