What is an emission factor? Where to find one and how to choose

An emission factor is the multiplier expressing how much greenhouse gas one unit of an activity releases. Every carbon calculation is fundamentally the same equation: activity data × emission factor = emissions. 12,000 kWh of electricity × 0.42 kg CO₂e/kWh = 5,040 kg CO₂e.

The left-hand side is usually solid — invoices, meters and delivery notes give you activity data. Most errors happen on the right.

The main sources

• IPCC guidelines — the basis of national inventories; default factors for fuel combustion
• National inventories and official publications — country-specific grid and fuel factors; the most accurate source for Turkey
• DEFRA / UK Government — a broad, annually updated set; widely used for transport and business travel
• LCI databases such as ecoinvent — cover all impact categories, not just greenhouse gases; the standard for LCA
• A supplier’s product footprint or EPD — the highest-quality source, specific to that supplier

Grid electricity: the most decisive factor

In energy-intensive processes electricity carries the result, and its factor varies severalfold by country. Depending on generation mix and year, Turkey’s grid factor sits around 0.40-0.45 kg CO₂e/kWh; a hydro-heavy Norwegian grid is a tenth of that, a coal-heavy grid twice as much.

Making the same product by the same process in two countries gives very different results purely because of the electricity factor. That is not a calculation detail but a direct input to supply chain decisions.

What to check when choosing a factor

• Unit match — kg CO₂e per kWh, per GJ, or per litre? Unit confusion is the most common error.
• Gases covered — CO₂ only or all greenhouse gases (CO₂e)? There is a few per cent between them.
• Geography — is the country or region right; a European average does not represent Turkey
• Year — grid factors change annually and must be consistent with your base year
• Boundary — combustion only, or does it include the fuel’s production and transport chain (well-to-tank)
• Calorific basis — lower or higher heating value; the gap can be ten per cent

Record the factor, not just the result

The most common documentation error is recording the result of a calculation but not which factor produced it. If the factor’s source, version and year are not on record the calculation cannot be reproduced — and that is the first thing a verifier will ask about.