# In what order does the Greenhouse Gas Protocol want me to try the four Scope 3 Category 1 methods for a purchased good?

Canonical: https://senseible.earth/answers/category-1-which-method-decision-tree-order

The Greenhouse Gas (GHG) Protocol's decision tree starts with screening: does the purchase matter to your Scope 3 or to supplier engagement? If yes, it asks for physical quantities, then product-level supplier data, then allocated Scope 1 and 2. If no, it picks average-data or spend-based.

## The tree, step by step

1. Screening: does this good or service contribute significantly to your Scope 3 emissions, or is supplier engagement otherwise relevant to your business goals?
2. If yes, do you have data on the physical quantity bought? If not, use the spend-based method.
3. If you have quantities, can the tier 1 supplier give product-level cradle-to-gate data of sufficient quality? If yes, use the supplier-specific method.
4. If not, can the supplier give allocated Scope 1 and 2 data of sufficient quality for the good? If yes, use the hybrid method. If not, use the average-data method.
5. If step 1 was a no, the tree only asks about quantities: with them, average-data; without them, spend-based.

## Rules around the tree

- The guide says companies need not always use the most specific method as a first preference.
- You may use different methods for different goods and services within Category 1, for example more specific methods for the categories that contribute most.
- The guide says collecting data from suppliers adds considerable time and cost, so companies should screen first to prioritise.
- Sufficient quality means the inventory most appropriately reflects your emissions, supports your business goals and serves the decisions of the people who use it.

## What decides each fork

Reading the tree as a whole (our reading): supplier data decides between the top three methods, and quantity data decides between average-data and spend-based. A buyer with tax invoices that show quantity and unit has the quantity data for most goods already, so spend-based is the fallback for services and items billed only in rupees.

## Four purchases of a fabricator, sent down the tree

- Steel plate: large share of purchases, tonnes on the invoice, mill gives no product figure and no allocated Scope 1 and 2: average-data
- Coated packaging film: large share, the supplier sends allocated Scope 1 and 2 for the film sold to you: hybrid
- Cutting oil: small share, litres on the invoice: average-data
- Courier fees: small share, only the rupee amount is known: spend-based

This is our reading of the guide's tree applied to example purchases. It carries no factors. A supplier that later sends a product-level figure of sufficient quality moves the steel or film up to supplier-specific.

## What Senseible does here

It does not choose a Category 1 method for you. Senseible keeps purchase invoices on the Scope 3 trail so the quantity each branch needs is on file.

- [Is a supplier figure always better than an average?](https://senseible.earth/answers/supplier-data-less-accurate-than-average)
- [Production and non-production purchases](https://senseible.earth/answers/production-vs-non-production-purchases)
- [Filling gaps in Scope 3 data](https://senseible.earth/answers/how-to-fill-gaps-in-scope-3-data)
- [Scope 3 supplier evidence](https://senseible.earth/scope-3-supplier-evidence)

Sources: [Greenhouse Gas Protocol Technical Guidance for Calculating Scope 3 Emissions, Category 1 (Figure 1.2 and the method summary)](https://ghgprotocol.org/sites/default/files/2022-12/Chapter1.pdf)

Last reviewed 2026-11-05. The tree is from Figure 1.2 as drawn in the guide. The purchases in the example are examples chosen to show the path.