What do I do when there is no emission factor for a material I buy?
Work down a ladder: ask the supplier for a product footprint, then look for a published factor for the same material, then use a documented proxy for a similar material, then fall back to a spend-based factor. If the line is small, you may exclude it with a stated reason. Never leave a guessed number unlabelled.
The ladder, best option first
- Supplier-specific data: an ISO 14067 product footprint or an environmental product declaration for the exact product.
- A published factor for the same material from a recognised database, matched as closely as possible on technology and region.
- A proxy: a factor for a similar material or a main ingredient, for example a generic polymer factor for a specialty compound. Write down why it is similar.
- Spend-based: rupees spent x an economic input-output factor for that product group. Fast, but an average across many products.
- Exclude, only if the purchase is small against your total and you state the reason and estimated size.
How to judge a proxy
The GHG Protocol Scope 3 Standard asks you to rate data on five indicators: technological, temporal and geographical representativeness, completeness, and reliability. A proxy usually scores poorly on technology. Record the score, so readers know which figures are weak and which to replace first.
Mistakes to avoid
- Using a factor in the wrong unit, such as a per-kg factor on a per-piece quantity.
- Mixing CO2-only factors with CO2e factors in one total without saying so.
- Using spend-based factors without adjusting for currency and price year, which can move results by a large margin.
- Filling the gap with zero. A line with no factor is a gap, not a zero.
What to record for every gap
- The material, quantity and spend.
- Which rung of the ladder you used, the factor, its source and year.
- The data quality rating and the plan to get better data, usually a supplier request.
What Senseible does here
Senseible follows a strict rule here: no factor, no figure. A purchase line with no matching factor is flagged in the supplier evidence trail and left without an emissions number, rather than filled with a guess. Choosing and documenting a proxy or spend-based factor is your decision.
Sources: GHG Protocol Corporate Value Chain (Scope 3) Standard (2011), Chapter 7: data quality, GHG Protocol Technical Guidance for Calculating Scope 3 Emissions (2013)
Last reviewed 2026-10-15.