What is Scope 3 Category 1?

Under the GHG Protocol, Scope 3 Category 1 covers cradle-to-gate emissions of all goods and services a company purchases. It is usually the largest part of a corporate footprint and the hardest to measure because it sits in the supply chain.

When should I use spend-based versus activity data?

Spend-based (EEIO) multiplies money spent by a sector emission intensity and is quick but coarse. Activity or average-data multiplies physical quantities by material factors and is more accurate. Start spend-based, then refine high-impact categories with activity data.

Are the default factors official?

No. The built-in factors are illustrative values representative of typical EEIO and DEFRA ranges so you can see the mechanics. Replace them with your required factor source — US EEIO, DEFRA, ecoinvent, or supplier-specific data — using the override field.

Why is spend-based estimation considered low quality?

It assumes every dollar in a sector has the same carbon intensity, ignoring efficient suppliers, recycled content, and price differences. It is acceptable for screening and prioritisation but should be upgraded for material categories before public reporting.

Does any data leave my browser?

No. The calculation runs entirely client-side in JavaScript. Nothing you type is transmitted, logged, or stored anywhere.

What is the Supply Chain Scope 3 Category 1 Estimator?

Estimate Scope 3 Category 1 purchased goods and services emissions using the spend-based (EEIO) or activity/average-data (DEFRA) method. Enter spend by sector or physical quantity, apply or override the emission factor, and read kgCO2e and tCO2e instantly in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Supply Chain Scope 3 Category 1 Estimator

Name: Supply Chain Scope 3 Category 1 Estimator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Scope 3 Category 1 — purchased goods and services — is typically the single largest slice of a company’s greenhouse-gas inventory, yet it lives in the supply chain where direct measurement is hard. This estimator implements the two standard GHG Protocol approaches so you can produce a defensible first number and then refine it.

How it works

The tool applies one of two formulas depending on the method you select:

spend-based (EEIO):   kgCO2e = spend × EEIO factor (kgCO2e per currency unit)
activity / average:   kgCO2e = quantity × material factor (kgCO2e per unit)
tonnes:               tCO2e  = kgCO2e / 1000

The spend-based method is fast because it only needs accounts-payable data, but it assumes a uniform carbon intensity per unit of money in each sector. The activity method multiplies a physical quantity — kilograms of steel, plastic, paper — by a per-unit emission factor, which removes the price distortion and is far more accurate.

Spend-based vs activity-based: the practical difference

The gap between the two methods can be dramatic because spend and physical quantity are not the same signal.

Consider a company that buys both recycled aluminium and virgin aluminium, paying the same price per kilogram for each (prices fluctuate but are broadly comparable). A spend-based EEIO estimate would assign the same emission factor to both purchases, missing the fact that recycled aluminium typically has a fraction of the carbon intensity of virgin aluminium. The activity method captures that difference precisely, because the material factors are specific to production route, not just sector.

This is why the GHG Protocol recommends a tiered approach: start with spend-based estimates to screen your entire supply chain, identify the top 10–15 purchase categories by estimated emissions, and then invest in upgrading those specific lines to activity-based data — either from supplier-provided lifecycle data or from authoritative databases.

Worked example

For illustration: a firm spending 250,000 currency units on primary metals at an illustrative EEIO factor of 1.05 kgCO2e per currency unit produces about 262 tCO2e for that line. The same firm, if it knows it bought 12,000 kg of virgin steel with an illustrative activity factor of 2.1 kgCO2e/kg, would record about 25 tCO2e — roughly ten times less. The enormous difference reflects both the difference in method and the different scope of what is being measured; spend-based factors typically embed more upstream processes.

Neither number is wrong — they measure slightly different things. The important practice is to document which method and which factor set you used, to be consistent year-over-year, and to upgrade high-impact lines to better data as your inventory matures.

Using the override field

The built-in factors are illustrative placeholders representative of published EEIO and DEFRA ranges. For any real inventory, replace them with the factor set your standard or framework requires: US EEIO, UK DEFRA conversion factors, ecoinvent, or supplier-specific Environmental Product Declarations. Enter your factor in the override field and the calculation updates immediately.