A supplier gave me its own emission factor for each material: how does the Greenhouse Gas Protocol's supplier-specific method add them, and what should come with each factor?

Multiply the quantity you bought by that supplier's product factor, then add the lines. The guide's construction example gives 145,000 kilograms. Ask each supplier for four things with each factor: life cycle emissions following the Greenhouse Gas Protocol Product Standard; method, data sources and global warming potential values; assurance; and other items such as the share of primary data.

The method in one line

The Greenhouse Gas (GHG) Protocol's supplier-specific method for Category 1 is quantity purchased times the supplier's cradle-to-gate factor for that product, summed over everything you buy. You need the quantity from your own records and a factor per product from the supplier. The guide's example of a suitable factor is one from a reliable cradle-to-gate inventory, for example one done with the GHG Protocol Product Standard.

What to ask for with each factor

The guide also says the supplier's data should, as far as possible, cover the same time interval as your inventory, and that verified data is preferred. It recommends also asking for the ratio of primary to secondary data so that you can track it as suppliers improve.

1. The product's life cycle emissions following the GHG Protocol Product Standard.
2. The method used and the data sources, including emission factors and global warming potential values.
3. Whether the data was assured or verified and, if so, what type of assurance.
4. Anything else relevant, for example the percentage of the product inventory calculated with primary data.

Two statements in the guide that pull in different directions

The supplier-specific method introduction says product-level data is the most accurate because it relates to the exact product and avoids allocation. Box 1.1 of the same chapter says supplier data may be less accurate than an industry average. The full comparison is on the page linked below.

If you are the supplier

Give your buyer the four items above with the number, not the number alone. That lets the buyer judge it against an industry average, which the guide says it may not beat (Box 1.1).

The guide's construction example, line by line

• Cement: 200,000 kilograms x 0.15 = 30,000
• Plaster: 600,000 x 0.10 = 60,000
• Paint: 200,000 x 0.10 = 20,000
• Timber: 100,000 x 0.25 = 25,000
• Concrete: 50,000 x 0.20 = 10,000
• Total: 30,000 + 60,000 + 20,000 + 25,000 + 10,000 = 145,000 kilograms of carbon dioxide equivalent (CO2e)

Quantities and factors are the guide's example values, which it says are not actual data. Do not use them as factors.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, which cover your own plant's energy. A product-level cradle-to-gate factor also needs your materials and your suppliers' data, which those records do not give.

• Is a supplier's figure better than an average?
• Which Category 1 method to use first
• Share of Scope 3 from supplier data
• Scope 3 supplier evidence

Sources: GHG Protocol Technical Guidance for Calculating Scope 3 Emissions, Category 1 (Purchased goods and services)

Last reviewed 2026-11-06. Based on the 2013 technical guidance. Ask your buyer which assurance type they accept before you commission any.