Hong Life CalculatorsUnderstanding the electricity CO₂ (Scope 2) calculator — concept and principle
This calculator estimates the greenhouse gas emissions caused by the electricity you use. In corporate carbon accounting these are called Scope 2 emissions: they happen at the power plant, not on your premises, but they are attributed to you because you consume the power. Households use the same calculation to estimate the footprint of their electricity bill.
How it is calculated
- Emissions (kg CO₂e) = electricity used (kWh) × grid emission factor (kg CO₂e/kWh)
- Tonnes = kg ÷ 1000
The electricity figure comes from your meter or bills, usually summed over a year. The emission factor is the average greenhouse gas intensity of the grid that supplies you. Note that 1 kg/kWh is the same as 1 t/MWh, which is how many national factors are published.
The principle
Each kilowatt-hour on a grid is produced by a mix of sources. Coal plants emit roughly 0.8–1.0 kg CO₂ per kWh, gas plants roughly half that, and nuclear, hydro, wind and solar almost nothing at the point of generation. The grid factor is the weighted average of that mix, so multiplying it by your consumption allocates to you a fair share of the power sector's emissions. The GHG Protocol Scope 2 Guidance calls this the location-based method. A second, market-based method uses the factor of the electricity you actually contract for, such as a renewable tariff or certificates, and companies are asked to report both.
Worked example
- Inputs: 3,500 kWh of electricity, grid factor 0.4 kg CO₂e/kWh.
- Emissions = 3,500 × 0.4 = 1,400 kg CO₂e.
- In tonnes: 1,400 ÷ 1000 = 1.4 t CO₂e.
| Electricity (kWh) | Emissions (kg CO₂e) |
|---|---|
| 875 | 350 |
| 1,750 | 700 |
| 2,625 | 1,050 |
| 3,500 | 1,400 |
| 4,375 | 1,750 |
| 5,250 | 2,100 |
| 7,000 | 2,800 |
How to read the result
The same consumption can produce very different emissions depending on where you live: from around 0.05 kg/kWh on hydro- or nuclear-dominated grids to about 0.8 kg/kWh on coal-heavy grids. To reduce the result you can use less electricity, shift to a cleaner supply contract (which changes the market-based figure), or generate your own renewable power. When comparing years, keep the factor year consistent, because national factors are updated as the mix changes.
Common mistakes
- Entering kW (power) instead of kWh (energy).
- Using a factor in g/kWh as if it were kg/kWh, a 1,000-fold error.
- Using a world average or another country's factor instead of your own grid's.
- Counting the same renewable certificates in both location- and market-based totals.
Frequently asked questions
Where do I find my country's grid factor?
National energy or environment agencies publish it, usually annually in t CO₂e/MWh; reporting programmes often specify which year to use.
Does the factor include transmission losses?
Usually not. Losses in the grid are counted separately under Scope 3 in the GHG Protocol.
Is CO₂e different from CO₂?
CO₂e also includes methane and nitrous oxide from power generation, weighted by their global warming potentials, so it is slightly higher than CO₂ alone.
Sources: World Resources Institute, GHG Protocol Scope 2 Guidance, 2015 · GHG Protocol, Corporate Accounting and Reporting Standard, revised edition