How to calculate your supplier carbon footprint when corporate customers demand it

Calculating a supplier carbon footprint is mostly disciplined bookkeeping plus transparent maths. You convert fuels, electricity, and other activities into tonnes of CO₂e using recognised emission factors.

Define the boundary

State which legal entities, sites, and time period you cover. Misaligned boundaries are the most common reason buyers reject a first submission.

Build the activity inventory

• Scope 1 fuels and process emissions
• Scope 2 purchased energy
• Agreed Scope 3 categories with the customer

Apply factors and quality checks

Use factors from reputable databases, match units carefully, and peer-check totals against energy spend so outliers stand out. Record every assumption.

Package the result

Provide scope totals, methodology notes, and the customer’s preferred template. Sustainly automates much of the factor application and export so SMEs can focus on data quality, not spreadsheet archaeology.