Product Carbon Footprint Requested by a Customer — Where to Start When None Has Been Calculated Before

An email arrives from a major customer. The subject line reads: "Supplier Carbon Data Request — Response Required by [Date]."

The attachment is a questionnaire. Page three asks for the product carbon footprint of every component supplied. In CO₂ equivalents. Per unit. Aligned with ISO 14067 or the GHG Protocol.

Nothing has been calculated before. No methodology is in place. No data has been collected. The deadline is six weeks away.

This moment is now one of the most common triggers for a first PCF calculation in manufacturing — and the instinct to panic is understandable. But the path from zero to a credible, submittable PCF is more structured than it appears. The steps are defined. The data sources are known. The standards are clear.

Here is exactly where to start.

Before collecting a single data point, it is essential to understand precisely what the customer is requesting — because "product carbon footprint" can mean different things in different contexts, and calculating the wrong thing is worse than calculating nothing.

A Product Carbon Footprint (PCF) quantifies greenhouse gas emissions, measured as carbon dioxide equivalent (CO₂e), associated with a product across defined lifecycle stages, which may include raw material extraction, production, distribution, use, and end-of-life.

However, most B2B customers requesting PCF data from suppliers are asking for a cradle-to-gate scope — not the full cradle-to-grave lifecycle. Cradle-to-gate assessments are useful for B2B manufacturers and when downstream data is limited — they include emissions from raw material extraction through manufacturing, ending at the factory gate.

A partial PCF encompasses the stages of extraction of resources, manufacturing of precursors, and production of the final product until it exits the company gate. This approach is widely considered to be the industry standard in calculating a PCF for B2B supply chain exchange.

Before beginning any calculation, confirm three things with the customer:

Confirming these upfront prevents the most common first-PCF mistake: producing a well-calculated result in the wrong format that cannot be used for the customer's purpose.

If a customer has asked for a PCF, the first step is selecting the most relevant standard. A standard details the exact boundaries, calculation steps, data requirements, and data quality considerations. Standards enable consistency and comparability of PCFs.

The two primary standards used across manufacturing are:

To help companies navigate the landscape of standards, the PACT Methodology introduces a hierarchy detailing which standards should be prioritized under which circumstances — companies should choose standards based on granularity, specificity to the product, and alignment with the PACT Methodology, industry expectations, and regulatory requirements.

In practice, for most manufacturing suppliers receiving a first-time customer request: follow the GHG Protocol Product Standard as the base, check whether a sector-specific Product Category Rule (PCR) exists for the product type, and confirm that the approach is PACT-aligned if the customer is part of a cross-industry supply chain transparency programme.

Once the standard is confirmed, two foundational decisions must be made before any data collection begins.

System boundary defines which lifecycle stages are included. For a B2B manufacturer responding to a customer request, cradle-to-gate is almost always the correct scope. Cradle-to-gate is primarily used for B2B products and measures greenhouse gas emissions from raw material extraction through to manufacturing, covering all emissions associated with the product until it reaches the factory gate.

Functional unit is the reference unit against which all emissions will be expressed — the denominator of the final PCF result. It must unambiguously define the product being assessed. For a component manufacturer, this is typically one unit of the product (one part, one kilogram, one batch) at a defined specification. The choice of boundary influences both the completeness and comparability of the PCF and should be transparently disclosed when reporting results.

Both decisions must be documented. They are not internal working choices — they are required disclosures in any PCF report submitted to a customer or auditor.

Data collection is typically the most resource-intensive stage of a PCF. The more primary activity data collected, the more accurate the PCF will be.

For a cradle-to-gate PCF covering material acquisition, pre-processing, and production, the data required falls into four categories:

The quality of a PCF directly depends on the quality of the data. Secondary data — sector averages from databases — is essential to initiate the process but introduces a margin of uncertainty. Primary data — real, specific data collected directly from the value chain — is the goal of a mature climate strategy.

For a first PCF, using secondary data from recognised databases such as ecoinvent, EPA, or DEFRA for material emission factors is entirely acceptable and standard practice. What matters is that the data sources are documented, the quality is disclosed, and the methodology is transparent. Once PCFs are calculated, companies should analyze the overall data quality and reliability — calculating the primary data share and data quality ratings — which reflect the underlying data quality and create a basis for decision-making and improvement over time.

With the BOM data in hand and the system boundary defined, each material and input must be matched to an emission factor — the numerical value representing the GHG intensity of producing one unit of that material.

The calculation involves listing all of the ingredients, materials, and activities needed to produce one item — BOM, site activities, supplier information — and multiplying each by the most relevant emission factor associated with the activity.

Emission factor databases used for this step include:

The matching process requires care. The emission factor selected must reflect the correct material grade, the correct production process, and — where possible — the correct geographic region. A global average emission factor for steel production will differ significantly from a region-specific factor that reflects a particular energy mix. A tonne of aluminium can range roughly between 4 and 18 tonnes of CO₂e in carbon intensity depending on the production process and electricity source. Using the wrong emission factor for a dominant material can shift the entire PCF result by a material amount.

To calculate the PCF, the formula is: activity data × emission factor for every activity, to develop the product's emissions inventory. Sum the results across all BOM inputs, energy consumption, transport, and waste to arrive at a total CO₂e figure per functional unit.

Before treating the number as final, three review steps matter:

No first PCF will have complete primary data across every input. This is normal and expected. The GHG Protocol and ISO 14067 both permit the use of secondary data and proxies where primary data is unavailable — provided the use of secondary data is disclosed and the data quality implications are reported.

When primary data is unavailable, secondary data from emissions databases or industry benchmarks can be used — however, secondary data reduces accuracy and should be flagged in the final assessment.

For missing supplier data, industry-average emission factors from ecoinvent or sector databases serve as the acceptable starting point. For missing energy data, regional grid emission factors provide a reasonable proxy. For components with unknown material composition, spend-based estimates may be used as a temporary proxy in screening calculations while primary data collection is pursued in parallel.

The important discipline is to flag every instance where secondary data or proxies were used, document the source, and build a data improvement plan that prioritises closing the highest-impact gaps in subsequent calculation cycles.

A first PCF calculated under time pressure, with secondary data and industry averages where primary data is unavailable, is still a legitimate and submittable result — provided the methodology is transparent and the data quality is disclosed.

The goal of a mature climate strategy is to progressively replace secondary data with primary data, thereby concretely engaging the supply chain. The first calculation establishes the baseline. Subsequent calculation cycles improve data quality, extend supplier-specific coverage, and refine the result. What matters most at the start is not perfection — it is a defensible methodology, complete documentation, and a clear plan for improvement.

Many first-time supplier requests do not require a fully verified third-party audited PCF, but they do expect a credible calculation based on a recognised standard with transparent methodology and data sources. They are expecting a credible attempt, built on a recognised standard, with the methodology documented and the data sources disclosed.

That is entirely achievable in a first calculation — and the steps above are how to get there.