Product carbon footprint methodology, step by step.

The most common objection to an automatic calculation is that it will end up using average data. This section explains why Xain’s method does not work like that: which data it uses, how it decides when in doubt and what you can check yourself.

How is a footprint built?

1. The product is identified from its technical documentation: drawings, data sheets, photos, manuals or the bill of materials.
2. It is broken down into a process tree: materials, operations (including their energy) and transport. Each type of product has its own structure.
3. Each node gets a physical factor, that is, kgCO₂e per physical unit of material, energy or transport.
4. When something is ambiguous the most conservative factor is applied, so the result is never understated.
5. Primary data from the customer or supplier replace generic data and refine the result.
6. The certificate shows the value, the traceability down to each node and a unique registration number.

Where do the factors come from?

From recognised life cycle and emission factor databases, such as ecoinvent, DEFRA/BEIS, worldsteel, AGRIBALYSE (ADEME) or ICE, from third-party environmental product declarations and category rules, and from Xain’s own physical library. Each node of the certificate states the factor it uses.

How accurate is it?

When the calculation starts from manufacturing technical documentation, the average deviation is 3.21 % against data measured at the factory. Accuracy rises with Xain’s levels: factors by category, country and product (Insight), technical data sheets (Precision) and primary data. The calculation adapts to the available data: without manufacturing detail it uses average physical factors in line with ISO 14067; with process data, the result is more precise.

Every footprint is an estimate

Any measurement of a product carbon footprint is, in reality, an estimate. There is no way to know with absolute precision the emissions of each concrete unit: even knowing a machine, you cannot know exactly how much it consumed to make one specific part that day. The same applies to transport.

The question is not whether a measurement is an estimate, but which methodology is used and how close it gets to reality. Until now, one of the most used methodologies for Scope 3 is spend-based calculation, which estimates emissions from the purchase amount and sector averages. For example, for “General furniture and related manufactures” an approximate factor of 0.642 kgCO₂e per euro spent may be used. With that method, a two-hundred-euro design chair would have ten times more emissions than a twenty-euro chair even if both were exactly the same, and it favours the cheaper supplier, even when it is not the more efficient one.

Xain uses a physical methodology in line with ISO 14067, verified by LRQA. Instead of starting from the amount paid, it breaks the product down into its physical elements and applies recognised physical emission factors. It is also an estimate — because no methodology knows the exact CO₂ of each unit — but one based on the physical characteristics and the process of the product, not on how much it cost. We detail it in physical versus spend-based factors.

Go deeper

This section has three pages: the ISO 14067 standard, the comparison between physical and spend-based factors and what the LRQA verification means.

What does each profile usually ask?

• Quality: which standard applies and who verified it? See ISO 14067 and the LRQA verification.
• Procurement: what data is used to calculate what I buy? See physical versus spend-based factors.
• Sustainability and ESG: can I audit the result? Every certificate lets you follow the calculation down to the factor of each node.