Scope 3 without the panic: a starting point for mid-sized companies

Most companies do not need a perfect Scope 3 inventory in their first year. They need a defensible screening estimate, an honest note about its limits, and a plan for improving it.

Why the first attempt goes wrong

The usual failure is ambition. A company decides to measure all fifteen Scope 3 categories at once, discovers that half of them require supplier data nobody will share, and abandons the exercise six months later with nothing usable. The second failure is the opposite: an estimate produced from a spend-based factor with no documentation, which collapses the first time somebody senior asks where the number came from.

Start with materiality, not completeness

For a typical mid-sized manufacturer, two or three categories account for most of the footprint — usually purchased goods and services, upstream freight, and either waste or business travel. Screening all fifteen categories at a coarse level tells you which ones matter. You then invest the effort where it changes the answer.

Run a coarse spend-based screen across every category.
Rank categories by estimated contribution.
Improve data quality only for the categories above roughly five per cent.
Document the screening method so next year's team can repeat it.

Spend-based factors are a starting point, not a destination

A spend-based estimate multiplies dollars by an industry-average intensity factor. It is defensible for a first screen and it is transparent, which matters more than precision at this stage. Its weakness is that it cannot detect improvement: if your supplier decarbonises, your number does not move. That is the reason to migrate material categories towards supplier-specific or activity-based data over two or three cycles.

What to ask suppliers, and when

Do not send a forty-question survey to two hundred suppliers. Identify the ten or fifteen that make up the bulk of your material spend, and ask them three things: do you have a published emissions figure, what is the boundary of it, and is it third-party checked. That letter gets answered. The forty-question survey does not.

Write the limitations down

Every inventory we produce carries a limitations section: which categories are screened rather than measured, which factors were used, which sites were extrapolated. Reviewers do not punish stated uncertainty. They punish discovering it themselves.

A realistic first-year plan

Weeks 1–2: set the organisational boundary and confirm the reporting year.
Weeks 3–5: gather Scope 1 and 2 data properly. This is the foundation, and it is usually available internally.
Weeks 6–8: coarse Scope 3 screen across all categories from finance and procurement data.
Weeks 9–10: improve the top two or three categories; draft the inventory with a clear limitations note.
Week 11: internal review and a one-page summary for the board or the lender.

That produces something you can stand behind, in a quarter, without a dedicated hire. Year two is where you tighten it.

Written by William Smith, Owner and Principal Consultant at Eco Sinergia LLC, Helena, Montana. Questions about anything above? Email info@eco-sinergia.org or call +1 917 480 5253.

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