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.

Supply Chain Scope 3 Category 1 Estimator

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.

Tips and example

A firm spending 250,000 currency units on primary metals at an EEIO factor of 1.05 kgCO2e per unit produces about 262.5 tCO2e for that line. The same firm, if it instead knows it bought 12,000 kg of virgin steel at 2.1 kgCO2e/kg, would book about 25.2 tCO2e — a very different answer that shows why activity data matters. Use the override field to drop in the exact factor your standard requires, and prioritise upgrading your highest-spend categories from spend-based to activity-based data first, since that is where the uncertainty is most material.