Supplier-specific data

A database gives you an average: steel sheet as it is typically made in a region. Your supplier makes it one particular way, with one particular energy supply. If their process is cleaner than average, a database will overstate your footprint. If it is dirtier, it will flatter you.

It is the same as costing from a list price versus a supplier’s quote. The quote is more accurate, as long as you check what it covers.

Primary and secondary data

• Primary data are measured or recorded for the specific process: your meter readings, your supplier’s production records, their verified footprint for the product you buy.
• Secondary data come from somewhere else: a database, a study, an industry average.

LCA 101 lesson 5 explained the usual split: primary data for the processes you control, secondary data for the rest. Supplier data sits in between. It is primary for the supplier, and it lets you replace a secondary dataset for one of your biggest inputs.

Many customers and standards now ask what share of a footprint is based on primary data. Supplier data is usually how you raise it.

Where supplier data comes from

Source	What it is	Strength	Watch out for
EPD	A verified, published LCA to a set of product category rules (PCR). See LCA 201 lesson 2 for how to read one.	Third-party verified, public, comparable within its PCR	Validity date, declared unit, which modules are included
Product carbon footprint (PCF)	A climate-only footprint, often to ISO 14067 or the GHG Protocol Product Standard	Often available when an EPD isn’t	May not be verified; methods vary between suppliers
Data exchanged through a shared format	A PCF sent in a standard data format between companies’ systems	Structured, machine-readable	Still only as good as the calculation behind it
Raw process data	The supplier’s energy use, material inputs and emissions for your product	Lets you model it yourself	Confidentiality; you need to do the modelling right

What to ask for

A vague request (“please send your carbon footprint”) gets a vague answer. Be specific.

1. Name the product. The exact product, grade or article number you buy, and the plant it comes from.
2. Name the unit. Per kg, per tonne, per m², per piece. Say which one you want.
3. Name the boundary. Usually cradle-to-gate: everything up to the product leaving their gate, including their suppliers.
4. Name the standard. For example “ISO 14067:2018” or “an EPD to EN 15804+A2”, or ask which standard they used.
5. Ask for the basis. Reference year, share of primary data, how electricity was counted (for example a grid average or a specific supply contract), and whether the figure was independently verified.
6. Ask for the document, not just the number. An EPD or a verified report you can cite beats a figure in an email.

How to check what comes back

Before you put a supplier figure into your inventory, run through this list. It takes a few minutes and catches most problems.

• Right product? Same grade, same plant, or clearly representative of what you buy.
• Right unit? If they declare per tonne and you model per kg, divide by 1,000. If they declare per m², you need thickness and density to convert.
• Right boundary? Cradle-to-gate for the product as you receive it. A figure for an intermediate product (a steel slab rather than finished sheet) leaves out processing steps.
• Current? Check the reference year, and for an EPD the validity date.
• Compatible method? The same impact method family as your study (for example IPCC AR6 GWP₁₀₀ values), and a compatible standard. An older EPD to a previous version of a standard may not be comparable.
• Verified? Independent verification is not always required, but it changes how much weight you can put on the number.
• Traceable? You can name the document, its issuer and the page or table where the number sits.

Don't cherry-pick

If you use a supplier figure because it is low, and a database average for another supplier because theirs is high, your result stops meaning anything. Apply the same rule to every input, and write the rule down.

Exercise

You buy the steel sheet for the panel in lesson 1 (5.0 kg bought per panel). The mill emails: “Our steel has a footprint of 900 kg CO₂-eq per tonne, cradle-to-gate, ISO 14067, reference year 2025.” A PDF report is attached; it states the product is “hot-rolled coil”.

1. Convert the figure to kg CO₂-eq per kg. What would the steel line in the panel inventory become, and what is the new total if everything else stays as in lesson 1?
2. Before you use it, what would you check or ask?

Answer

1. 900 kg per tonne ÷ 1,000 = 0.9 kg CO₂-eq per kg. Steel line: 5.0 × 0.9 = 4.5 kg CO₂-eq (instead of 9.928). New total: 12.581 − 9.928 + 4.5 = 7.153 kg CO₂-eq per panel. That is a 43% drop, which is exactly why you check before you use it.
2. The key question is the boundary. Hot-rolled coil is not necessarily the sheet you buy: if your sheet is cold-rolled or coated after the coil stage, those steps are missing. Ask for the figure for the product as delivered, or add the missing steps from a database and say so. Also check that the report is verified (or who prepared it), how electricity was counted, which GWP values were used, and that the figure covers the plant you actually buy from. Then keep the PDF as your evidence.

What you should now be able to do

• Explain the difference between primary and secondary data, and where supplier data fits.
• Write a specific data request to a supplier.
• Check a supplier’s figure for product, unit, boundary, date, method and verification before using it.
• Explain why the same rule has to apply to every supplier.

Sources

• ISO 14044:2006, data collection and data quality, iso.org.
• ISO 14067:2018, carbon footprint of products, iso.org.
• All example figures: hypothetical, created for this lesson.

Checked: 2026-09-29