How to Calculate a Product Carbon Footprint Under PACT v3

Customers that track Scope 3 increasingly ask suppliers for the carbon footprint of each product they buy, and many of those requests name PACT. The Partnership for Carbon Transparency, hosted by WBCSD, publishes two documents that work together: the PACT Methodology, which says how to calculate a product carbon footprint (PCF), and the Technical Specifications, which say how software exchanges it. This guide covers the methodology, version 3.0, released on 30 April 2025, with a worked example. The rules are the same wherever your plant is.

What a PACT footprint covers

• Cradle-to-gate. All upstream stages up to your production gate: raw materials, their transport to you, and your own manufacturing. Product use and end-of-life are excluded.
• Per declared unit. The footprint is kg CO2e per unit of product, for example per kilogram or per piece, from the list of accepted declared units.
• All greenhouse gases, converted with 100-year global warming potentials from the latest IPCC assessment report.
• Transport inside the boundary counts on a well-to-wheel basis, the fuel and the energy of storage, but not the manufacture of the vehicles. Outbound logistics to your customer is reported separately.
• Validity of up to three years, provided the production process does not change by 10% or more in that time.

Step 1: map the processes and collect the data

List every process inside the boundary and the data each needs: the activity (litres of fuel, kWh, kilograms of each material) and an emission factor for it. PACT defines both as primary or secondary. Primary activity data is measured at your own sites, for example from utility bills, meters or energy management software. A primary emission factor comes from your own operations, such as direct combustion emissions or a factor based on stoichiometry. Default factors, industry averages, government statistics and input-output databases are secondary.

Step 2: allocate only when you must

Most plants make more than one product on shared equipment, so plant-level emissions have to be shared between them. PACT v3 sets a hierarchy:

1. Avoid allocation. Sub-divide the process so each product's own inputs are counted directly, for example materials from the bill of materials. System expansion is allowed only where there is a dominant, identifiable displaced product with sector consensus.
2. Check the ratio of economic value between the co-products. If it is above 5, use economic allocation.
3. Otherwise use a physical relationship, such as mass, where one exists. In doubt, PACT says mass should be prioritised. If there is no physical relationship, use economic allocation.

Sector rules (product category rules or sector guidance) take precedence where they exist and meet PACT's safeguards.

Worked example: one plant, two products

An illustrative plant makes 6,000 tonnes of product A and 4,000 tonnes of product B in 2025 on shared lines. The value per tonne of the two products differs by less than a factor of 5, and both are sold by weight, so shared emissions are allocated by mass (60% to A, 40% to B). Materials are counted directly from each product's bill of materials, so they need no allocation.

Dividing by production gives the footprint per declared unit of 1 kg: product A is 13,800 t ÷ 6,000 t = 2.30 kg CO2e per kg, and product B is 11,600 t ÷ 4,000 t = 2.90 kg CO2e per kg. B is higher because its materials are more carbon-intensive, which the bill-of-materials step keeps visible. A plant-wide average of 2.54 would have hidden it.

Step 3: calculate the primary data share

The primary data share (PDS) is the percentage of the footprint calculated with primary data. Each component's absolute emissions are weighted by its own PDS. An input counts as primary only when both its activity data and its emission factor are primary. If a component's PDS is unknown, for example a supplier that did not send one, it counts as 0%.

Product A's PDS is 2,880 ÷ 13,800 = 20.9%. Two things stand out. Electricity is 15% of the footprint but counts as secondary, because the grid-average factor is a published average, even though the kWh are metered. And the fastest way to raise PDS is upstream: every supplier that sends a PCF with a higher PDS of its own raises yours.

Step 4: what goes to your customer

Through a PACT conformant solution, the footprint travels as a structured record, not a PDF. In the Technical Specifications v3.0 the key fields include the footprint excluding biogenic uptake (pcfExcludingBiogenicUptake), the declared unit (declaredUnitOfMeasurement and declaredUnitAmount), the product mass per declared unit, the reference period, the primary data share and the cross-sectoral standards used. Your customer's software reads those fields directly, so nobody re-keys a number.

How PACT relates to ISO 14067 and the GHG Protocol

PACT builds on the GHG Protocol Product Standard and ISO 14067, and narrows them where they leave choices open: the boundary is fixed at cradle-to-gate, the allocation order is set, and data quality must be reported in the same way by everyone. A PACT footprint can therefore also be described against those standards, but not every ISO 14067 study is PACT conformant. See ISO 14064 vs ISO 14067 vs the GHG Protocol for how the standards fit together.

A checklist before you send a footprint

• The boundary is cradle-to-gate and every excluded process is listed, adding up to under 3%.
• The declared unit matches what the customer buys (per kg, per piece, per litre).
• Allocation follows the hierarchy, and the basis (mass, economic value) is written down.
• Each component records whether its activity data and factor are primary or secondary.
• Supplier PCFs carry their own PDS; unknown ones are counted at 0%.
• The reference period and validity are stated, and you know what change would trigger a recalculation.

ZeroCarbon is a PACT conformant solution for Technical Specifications v3.0. It calculates each product's footprint from a ledger of your bills and production records, records the allocation used, and publishes the footprint only to customers you grant access. If a customer has asked you for a PACT footprint, tell us who is asking and we will set up a workspace to answer it.