A product carbon footprint (PCF) is the greenhouse gas emissions of one unit of a product, reported in kgCO2e. When a customer asks a component supplier for one, it almost always means cradle-to-gate: emissions from raw material extraction to the supplier's factory gate, excluding customer use and end-of-life, because the supplier cannot know how the part will be used.
The request usually shows up as a line in a supplier questionnaire or a new field in a customer portal. How good your answer is depends on the plant floor: how your electricity is metered, how your bill of materials is sourced, and how you split shared energy across hundreds of part numbers. This guide covers the rulebooks behind the request, the boundary you are expected to draw, the data fields a customer's system will read, and the allocation choices an auditor will ask you to explain.
Why a supplier's answer is cradle-to-gate
The GHG Protocol Product Standard allows a cradle-to-gate inventory for intermediate products whose final use is unknown. Its standard example is an aluminum ingot, which can become a beverage can, a window frame or an engine block. A bracket, a casting or a molded housing is in the same position. Any life-cycle stage you leave out has to be disclosed and justified. A comparison of the major protocols by Wang, Wang and Yang (2018) found that ISO 14067, the GHG Protocol and PAS 2050 all permit cradle-to-gate assessment.
The rulebook stack: ask which one applies before you calculate
PCF rules come in layers, and each layer narrows the one above it.
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General standards. ISO 14067:2018 sets principles, requirements and guidelines for quantifying and reporting a product's carbon footprint, consistent with the ISO 14040/14044 life cycle assessment standards. It explicitly covers partial footprints such as cradle-to-gate. It addresses climate change only and leaves offsetting and communication out of scope. The GHG Protocol Product Standard sits next to it.
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Cross-sector exchange method. WBCSD's Partnership for Carbon Transparency (PACT) released PACT Methodology Version 3 on 30 April 2025 and withdrew V2. PCFs already calculated under V2 stay valid for three years. Recalculation is triggered earlier by a major process change exceeding 10% or by a product containing more than 5% biogenic carbon.
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Sector rulebooks. In automotive, the Catena-X standard CX-0136 Use Case PCF states that "the methodology used for calculating a PCF MUST be conformant with Product Carbon Footprint Rulebook V4," and excludes use-phase and end-of-life emissions. In chemicals, the Together for Sustainability (TfS) PCF Guideline fills the same role.
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Data format. The PACT Technical Specifications for PCF Data Exchange (v3.0.3, 18 November 2025) define the fields your PCF must contain when it passes from your system to your customer's.
Carbon-accounting software company Tanso reports that Catena-X PCF Rulebook v4 was published in September 2025. Tanso describes it as prescribing a uniform cradle-to-gate boundary and setting binding specifications "where ISO deliberately leaves room for interpretation." That is the practical reason to ask your customer which rulebook they require before you start. A footprint that conforms to ISO 14067 in general can still be rejected if it does not follow the specific choices of the customer's sector rulebook.
The sector bodies say they are converging. TfS said in a January 2025 news post that its guideline update improved "definitions for waste and decisions in multi-output processes," aligned data quality ratings across frameworks, and synchronized with WBCSD PACT, Catena-X and the Global Battery Alliance. CO2 AI, a carbon-accounting vendor, reports that the TfS v3.0 allocation hierarchy is "in complete alignment with Catena-X and WBCSD PACT."
Drawing the boundary
For a typical component supplier, a cradle-to-gate boundary includes:
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Extraction and processing of raw materials, plus the upstream footprint of purchased parts.
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Inbound transport of those materials and parts.
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Your own gate-to-gate processes: machining, forming, heat treatment, coating, assembly, and the utilities and buildings that support them.
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Storage and movement between stages. PACT's methodology page says its cradle-to-gate boundary "contains product storage and shipping processes, including transportation within and between the life cycle stages."
Outbound logistics to the customer is calculated separately under PACT and is not part of the cradle-to-gate figure. Use and end-of-life are out. The PACT tech spec also asks for a description of the processes included in each life-cycle stage. Write down what is in and what is out, and for each exclusion give a reason an auditor would accept.
Declared unit and reference period
Every PCF is stated per declared unit. For discrete parts that is usually one piece. For bulk or semi-finished material it is usually one kilogram. The PACT tech spec requires the figure excluding biogenic CO2 uptake (pcfExcludingBiogenicUptake, in kgCO2e per declared unit). It also requires a reference period: the start and end dates of the activity data behind the number. If your figure uses a calendar year of utility bills and production counts, those are the dates you report. If a process changes significantly partway through, the reference period determines what the footprint actually represents.
Primary data, data quality and the 2027 deadline
Wang, Wang and Yang define primary data as direct measurements and secondary data as what you use when primary data is not available. On the floor, primary data is your metered kWh and therm readings, your actual material consumption and your supplier-specific footprints. Secondary data is database or industry-average emission factors.
Two fields in the PACT tech spec turn this distinction into numbers a customer can compare across suppliers:
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Primary data share (primaryDataShare, SHALL be reported): the "share of primary data in the final absolute PCF value excluding biogenic CO2 uptake," as a percentage. CO2 AI gives the TfS formula as PDS = (Sum of |Impact Contribution| × PDS of each input) / Total PCF. Each input is therefore weighted by its contribution to the footprint and by its own primary data share. A supplier-specific PCF with high primary content raises your score. An industry-average factor for the same material does not.
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Data quality ratings (SHALL): technologicalDQR, geographicalDQR and temporalDQR, each scored from 1 to 5 as a weighted average across all inputs. PACT's own breakdown of the V3 updates notes that this five-level scale replaced the previous three-level system.
These fields are not optional for much longer. Tanso reports that under Catena-X, primary data share and DQR become mandatory after a transition phase ending in 2027. CO2 AI reports the same 2027 timing for TfS, with voluntary reporting until then. Tanso also reports that Catena-X registration became "an official part of BMW's procurement process" in April 2025, and that Volkswagen, Mercedes-Benz and Ford followed. For automotive suppliers, the quality of this data is already part of sourcing decisions.
Where the numbers come from in a real plant
A defensible PCF draws on four data streams:
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Bill of materials with sourced weights. For many components, purchased material is typically a large share of the total. Use gross input weights, not finished part weights (see the section on scrap below).
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Supplier-specific PCFs. Request them from your mill, resin supplier, forge or casting house, preferably in the PACT format so the primary data share and DQR carry through. Each supplier PCF you get in place of an average factor improves both your number and its credibility.
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Metered energy. Electricity, natural gas and any other fuels, ideally metered below the utility meter.
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Production data. Good-part counts, run times and downtime by machine and part number, usually from MES or the ERP routing.
The fourth stream is the one most plants underuse. A Factory-X "PCF Guidance" document, announced by Fraunhofer IWU on August 6, 2026 with contributors including ESTAINIUM and Siemens, recommends "spatial and temporal process separation through submetering, combined with production data, thereby reducing reliance on estimates." In practice, that means a machine-level or line-level meter timestamped against the same clock as your production records. You can then tell which part number was running when the energy was drawn.
Allocating plant energy across part numbers
Most plants run many products through shared equipment and shared buildings, so some emissions have to be divided. The GHG Protocol Product Standard's order of preference, as tabulated by Wang, Wang and Yang, is:
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Avoid allocation by subdividing processes, redefining the functional unit, or expanding the system.
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Use physical relationships.
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Use economic or other allocation methods.
PACT V3, according to PACT's own summary, "includes a new decision tree to guide the allocation process." The Factory-X guidance covers how emissions "can be distributed within multi-product manufacturing environments using process subdivision, system expansion, or allocation methods." It gives "practical examples of allocating building-related emissions, downtime-related emissions, and machine energy consumption."
Applied to a job shop or a tier-2 line, that hierarchy usually looks like this:
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Subdivide first. Submetering is how you subdivide. If a machining cell has its own meter and you know which jobs ran on it and when, most of that cell's energy is attributed directly and never has to be allocated.
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Then use a physical basis. Where energy is still shared, divide it on a physical relationship you can measure and defend, such as output mass or recorded machine time. Choose the basis that tracks what drives the energy use on that asset.
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Handle idle time and overhead separately. Energy drawn during downtime and warm-up, and building loads like HVAC, lighting and compressed air, do not behave like cutting energy. The Factory-X examples treat them as separate categories. Your method should do the same, not fold them silently into per-part machine energy.
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Use economic allocation last. Splitting by revenue is easy to calculate, but it sits at the bottom of the hierarchy. Expect to explain why a physical basis was not workable.
Whatever method you use, write it down. The PACT tech spec field allocationRulesDescription (SHOULD) asks for a "description of the allocation rules applied to the PCFs foreground data including an explanation of the underlying reasons." Customers will ask about this, and auditors will compare it with what your spreadsheet actually does.
Scrap: gross input, and the co-product question
The most common error on the floor is building the footprint from finished part weight. A machined part that begins as a heavier bar or billet carries the footprint of the whole bar, because you bought and processed the whole bar. Start from gross material input, including chips, trim, runners and rejects.
Next, decide how the scrap leaving your dock is treated. PACT V3 "clarifies how to distinguish co-products from waste" as part of its allocation decision tree, and TfS says its update improved definitions for waste and multi-output decisions. The Factory-X guidance also addresses scrap, packaging and transportation, with worked examples for a milled component, a forged component and an additively manufactured suspension fork.
Recycled material is where rulebooks differ most. Under a cut-off approach, in general terms, the product that generates the scrap does not take credit for its later recycling, and the product that uses recycled content carries the burden of the recycling process but not the original production. Other approaches share burdens and credits differently. Your customer's rulebook decides which approach applies, so confirm it before you set up a scrap-credit line in your model.
Electricity: grid average or contract
For many metal-cutting and forming plants, electricity is the largest emission source inside the gate. You can apply either a grid-average emission factor for your region or a contract-based factor that reflects renewable energy purchases, energy attribute certificates or supply contracts. The two can produce very different footprints for the same physical kWh. That is why customers ask which one you used.
PACT V3 provides what PACT's own article calls "high-level guidance" on electricity and contractual instruments such as RECs and Guarantees of Origin. Before a certificate purchase counts toward a customer-facing PCF, check the conditions in the specific rulebook your customer requires. Either way, disclose the basis so the number can be compared with other suppliers'.
Verification
Third-party verification information is optional (MAY) in the PACT data-exchange spec, but that is changing. According to PACT, companies may pursue verification of their PCF calculation model until 2030. After that, the requirement shifts toward verification of the PCF program. The Catena-X rulebook library lists a PCF Verification and Certification Framework v2.0 alongside PCF Rulebook v4.0. A calculation model that is built once, documented and verified scales across part numbers far better than a series of one-off spreadsheets.
The operator's takeaway: this is a metering and data project
A credible PCF depends less on carbon accounting skill than on plant data infrastructure. The spending usually goes to three places: machine- or line-level submetering, linking those meters to MES or production counts, and a structured supplier request program for material PCFs. Compare those costs with the risk of being scored below a competitor on primary data share and DQR once those fields are mandatory in 2027. For suppliers selling into OEMs that have made Catena-X registration part of procurement, that comparison drives the budget case.
Pre-2027 checklist
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Rulebook: Confirm with each major customer whether they require PACT V3, Catena-X Rulebook V4 or TfS.
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Declared unit: One piece or one kilogram, applied consistently across the product family.
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Boundary: Cradle-to-gate with inbound and internal transport and storage. Outbound delivery reported separately. Exclusions documented and justified.
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Reference period: Start and end dates for all activity data.
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Metering: Submeters on the highest-load assets, time-aligned with production data.
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Allocation rule: Subdivide, then physical, then economic. Idle and building loads handled separately. Reasoning recorded for allocationRulesDescription.
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Scrap: Gross material input. Co-product versus waste decision recorded. Recycling approach matched to the rulebook.
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Electricity factor: Grid-average or contract-based, disclosed.
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Primary data share and DQR: Calculated now, even while voluntary, so you know where you stand.
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Verification: Plan for calculation-model verification and track the Catena-X framework if you sell into automotive.
Related reading
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Sources
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PACT Standard V3 is Here: A Breakdown of the Major Updates, PACT Insights
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Technical Specifications for PCF Data Exchange (Version 3.0.3)
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ISO 14067:2018, Carbon Footprint of Products Standard Revised, ANSI Blog
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Calculating the Carbon Footprint of an Industrial Product, Fraunhofer IWU
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Catena-X for automotive suppliers: PCF requirements and Rulebook v4, Tanso
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What you need to know about TfS PCF Guidelines Version 3.0, CO2 AI
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TfS announces new updates to the PCF Guideline, TfS Initiative