Spend-based Scope 3: what it tells you and what it does not

4 min read · Updated 23 settembre 2026

Scope 3 is the emissions that arise elsewhere: at suppliers, in transport, in the use of products. For a small company an exact calculation is usually impossible — the supplier data does not exist. Hence the spend-based estimate: how much money you spent in a purchasing category, multiplied by that category's average emission factor.

What such an estimate tells you

• The order of magnitude. Whether purchasing is ten times your own emissions or comparable with them.
• Where to look first. The category with the largest spend is usually the largest source, and that answers the question of what to work on at all.
• A starting point with suppliers. Asking one large supplier is sensible; asking all of them is a wasted month.

What it does not tell you

• Nothing about your particular supplier. The factor is an industry average; a supplier running on renewable electricity and one running on coal get the same number.
• Nothing about improvement. Buy the same goods cheaper next year and the estimate falls while the emissions do not. A spend-based figure is therefore unfit for measuring progress.
• Nothing about precision. The deviation can be large in either direction, and that is a property of the method, not a data-entry mistake.

Why it stands apart from Scope 1 and 2

Because it is a different kind of figure. Scope 1 and 2 are computed from consumption you can show on an invoice; spend-based Scope 3 is an estimate from averages. Adding them together would produce one number that is neither measured nor estimated, and neither half would be visible any more. In the report they therefore stand separately, and the estimate is marked as an estimate.

When to do it anyway

When somebody asks for Scope 3 and you have nothing. An estimate with a stated method is a better answer than an empty field — provided it is labelled as an estimate and says what it was built from.