How to calculate Scope 3 Category 1, step by step.

Category 1 covers the cradle-to-gate emissions of the goods and services you buy in the period you report. It is one of the 15 Scope 3 categories of the GHG Protocol and, for many companies, one of the most relevant.

Which methods are there?

The GHG Protocol describes four approaches, from most to least specific:

Method	What it uses	Advantage	Limit
Supplier-specific data	Emissions of the product or the supplier	Reflects the real product	Requires the supplier to have and share the figure
Hybrid	Supplier data where available and estimates where not	Balance between effort and accuracy	Mixes data qualities
Average data	Physical quantities times average emission factors	Does not depend on price	Needs to know what and how much you buy
Spend-based	Amount times an economic factor	Only needs invoices	The footprint rises with the price

What are the steps?

1. Define the period and boundaries: which entities and which year are included.
2. List the purchases from the ERP or accounting, separating goods and services.
3. Prioritise the lines that weigh most in volume or spend, because that is where the data improves most.
4. Choose the method for each line: the most specific one you can sustain.
5. Gather the information: materials, weights, processes or technical sheets for physical lines.
6. Apply the emission factors and add up in tCO₂e.
7. Document the method, factors and assumptions so you can repeat and justify it.
8. Improve every year by replacing average data with primary data on the biggest lines.

When does each method fit?

Start with spend if you only have invoices, but use it as a first snapshot and not as the basis for decisions about products. As soon as you know which lines weigh most, move to physical factors and, if possible, to supplier data. We explain it in physical versus spend-based factors.

How does Xain help?

Xain calculates Category 1 with physical factors from your purchase lines and technical documentation. It takes less than 10 minutes of your work and results arrive in 1 to 2 weeks. You can see how it works in Scope 3 for purchases. Xain also covers Category 2 (capital goods) with the same physical method.