How to calculate a product carbon footprint

What a product carbon footprint is

A product carbon footprint is the total greenhouse gas emissions of one product over all or part of its life, stated in kilograms of carbon dioxide equivalent (kg CO₂e) per unit. The unit might be one part, one kilogram or one litre.

Your customer usually asks because your product is one of their purchased goods. Many companies first estimate those emissions from what they spend, using an average per pound for each type of purchase. A spend-based average cannot tell one supplier from another. Your own figure replaces that average, so any improvement you make shows up in their numbers.

A product footprint is often confused with two other measures. This is how they differ.

A good corporate footprint is the best starting point. The energy, fuel and transport data in it has already been collected and checked, so you are not starting from nothing.

Step 1: choose the rules

Agree the method with your customer before you calculate anything. Rework after the numbers are done is a common cause of delay, and it is avoidable.

The standards you will meet most often are these:

• ISO 14067:2018, the international standard for quantifying the carbon footprint of products.
• The GHG Protocol Product Life Cycle Accounting and Reporting Standard, published in 2011 by the World Resources Institute and the World Business Council for Sustainable Development (WBCSD).
• The PACT Methodology from WBCSD's Partnership for Carbon Transparency. Version 3.0 was published in 2025. It is built for exchanging cradle-to-gate footprints between companies, and some large buyers ask suppliers to follow it.

Where a product category rule (PCR) or sector guideline exists for your product, customers and verifiers will usually expect you to follow it. PACT sets an order: product category rules first, then sector guidance, then PACT itself, using the specific rules only where they align with PACT.

Step 2: pick the product, the unit and the boundary

You cannot footprint everything at once. Start with one product: one your customer has asked about, one you sell in high volume, or one made from carbon-intensive materials such as steel, aluminium, cement or plastics. One product teaches you the process before you repeat it.

Describe the product precisely: its specification, the stock codes it covers and the site where it is made. If one footprint is to stand for a group of stock codes, show that they share the same materials and processing.

The unit

For a part sold to another business and assessed to your gate, use a declared unit, such as one bracket or one kilogram of product. For a finished product assessed over its whole life, ISO 14067 uses a functional unit, which describes what the product does and for how long.

The boundary

Most business customers ask for cradle-to-gate: from extracting raw materials to your product leaving your site. PACT is built around this boundary. It includes:

• Raw materials and bought-in components, including the emissions of making them.
• Transport of those materials to your site.
• Your own production: energy, fuels, process emissions, refrigerants and scrap.
• Packaging.

Distribution after your gate, the use of the product and its end of life sit outside a cradle-to-gate footprint. Under PACT, outbound transport is still worked out and reported separately, up to the point where your customer takes responsibility for it.

Set the reference period too, usually your latest full year of production, and check it is typical of how you normally run.

Step 3: collect the data

This is where most of the time goes, and where the quality of the result is decided. Every footprint mixes two kinds of data.

• Primary data is specific to your product and supply chain: metered energy at your site, the weight of each material, a supplier's own product footprint.
• Secondary data comes from databases and industry averages. Use it to fill gaps, and record which figures are estimates.

For one product, gather:

• The bill of materials, with the weight of every material and component.
• Process scrap and yield at each stage.
• Energy used by the processes that make the product.
• Packaging materials and weights.
• Inbound transport for the main materials: distance, mode and load.
• Supplier footprints for materials, where suppliers can give them.
• An emission factor for everything else, with its source, version and year.

Few sites meter each product. Share site energy using a driver that reflects how the product uses it, such as machine hours for machining or mass for melting. Record the method and use it every time.

For UK activity, the government's greenhouse gas conversion factors from the Department for Energy Security and Net Zero (DESNZ) are widely used. For India, the Central Electricity Authority publishes the grid electricity factor. Material factors usually come from life cycle databases, some of them paid. See how we handle emission factors.

Step 4: calculate and share out common emissions

For each input, multiply the activity data by its emission factor, then add up the lines. Each line should show its quantity, factor and source, so anyone can follow the arithmetic.

Work per declared unit. For a steel bracket, that means the weight of steel in one bracket plus its share of scrap, times a factor for steel. Do the same for the coating, the share of site energy, inbound transport and packaging, then add the lines.

Sort the lines from largest to smallest when you finish. The biggest lines tell you where better data, and reductions, will count most. In manufactured parts they are often the bought-in metals, plastics or chemicals.

When one process makes several products

A heat treatment run or a moulding run often serves more than one product, so its emissions have to be shared. PACT sets a fixed order:

1. 1Avoid allocationSplit the process into parts that each serve one product, if you can.
2. 2Compare valuesDivide the market value of the highest-value co-product by that of the lowest-value one.
3. 3Choose the methodIf that ratio is 5 or less, share by a physical measure such as mass. If it is more than 5, share by economic value.

Scrap, offcuts and rejects are usually treated as waste, so they carry no share. PACT sets four tests for a co-product. Its further use must be certain, it must need no more than normal industrial processing, it must come out of the core process, and its use must be lawful. Use one allocation method within a footprint and write down why you chose it.

Step 5: rate the data and share the result

Your customer will want to know how far to rely on your figure. PACT sets two measures to travel with every footprint. The primary data share is required now, and data quality ratings are required from 2027.

• The primary data share: the proportion of the footprint's emissions calculated from primary data. If your only primary data is your own metered energy and the materials come from database averages, the share will be low.
• Data quality ratings: each dataset is rated from 1 (best) to 5 (worst) on how well it matches the real process in technology, geography and time. The ratings are then combined into one for the footprint.

Neither is a pass mark. Both are there so your customer can judge the figure, and both should improve each year. The quickest way to raise your primary data share is to ask the suppliers of your largest materials for their own product footprints.

When you share the footprint, send it with its declared unit, reference period, primary data share, data quality rating and the standard it follows. PACT also publishes technical specifications so footprints can pass between companies' systems in one format.

Under PACT a footprint stays valid for up to three years, unless something changes it by 10% or more, when you should recalculate. If your customer wants the figure independently checked, read getting a product footprint ready for assurance.

How ESGen helps

Carbon per product is a service our team scopes with you. It is not a feature of the ESGen platform. If your sites are in the platform, the electricity, gas and fuel figures for each site are already there with the bill and emission factor behind each one, and our team shares them across products using a driver such as parts made or machine hours.

We follow the standard your customer names, such as ISO 14067 or the PACT Methodology, and we keep the evidence file a verifier would ask for. We do not verify or certify footprints; independent verifiers do. Read more on product footprints, or book a demo and bring the request your customer sent you.