Scope 3 Emissions Explained: The 15 Categories, Examples and How to Calculate Them

If a customer, a bank or the Science Based Targets initiative has asked your company about “Scope 3”, you are not alone. Scope 3 is where most of a company’s climate impact actually sits, and it is also the part most businesses have never measured. This guide explains the 15 categories in plain English, with examples for small and medium businesses, and shows how to calculate them without an expensive software platform.

I am an environmental engineer and I prepare greenhouse gas inventories following the GHG Protocol. Everything below follows the GHG Protocol Corporate Value Chain (Scope 3) Standard, the framework used by SBTi, CDP and most reporting rules.

Scope 1, 2 and 3: the quick definitions

Scope 1 covers direct emissions from sources you own or control: fuel burned in your boilers, generators and vehicles, plus refrigerant leaks. Scope 2 covers the emissions from electricity, heat or steam you buy. Scope 3 is everything else in your value chain, from the materials your suppliers make to the use and disposal of the products you sell.

The 15 Scope 3 categories, with examples

Which Scope 3 categories matter most?

It depends on what you do. For a manufacturer or product brand, Category 1 (purchased goods) is usually the largest by far, followed by transport and, for energy-using products, Category 11 (use of sold products). For a consultancy, agency or events company, business travel, purchased services and commuting dominate. For a retailer, it is the products on the shelves. Banks and investors are the exception: Category 15 (financed emissions) can dwarf everything else.

The GHG Protocol asks you to screen all 15 categories, explain any you exclude, and focus effort on the ones that are large, that you can influence, or that stakeholders care about. Under SBTi’s SME route, small companies commit to measure and reduce Scope 3 without setting a numerical target for it, which makes a good first screening the most useful step.

How to calculate Scope 3 emissions

There are four main methods, from quickest to most accurate:

Spend-based: multiply what you spent in each category by an emission factor per currency unit (for example, kg CO₂e per dollar spent on IT services). Fast, uses your accounts data, but approximate. Average-data: use quantities instead of money, such as tonnes of steel or kilometres travelled, multiplied by average emission factors. More accurate for materials and transport. Supplier-specific: use emissions data reported by your actual suppliers. The most accurate, but needs supplier cooperation. Hybrid: combine supplier data where you have it with average or spend data for the rest. This is what most companies end up doing.

A practical first year for a small business looks like this: export a year of spending from your accounts, map each supplier to a category, apply spend-based factors to get a first estimate, then replace the biggest few lines with activity data (kilograms, kilometres, kilowatt-hours). That alone usually gives a reliable picture of where most of your emissions are.

How to calculate the carbon footprint of a company

A full company footprint adds Scopes 1, 2 and 3 for the same year. Collect fuel and refrigerant data for Scope 1, electricity bills for Scope 2 (reported both location-based and market-based), and the Scope 3 categories above. Choose emission factors from a recognised source (such as the UK government conversion factors, the US EPA or the IPCC) and document every assumption so next year’s numbers are comparable. You can see a worked example in this sample GHG inventory for a small guesthouse.

You cannot reduce what you have not measured, and for most companies the biggest number is the one they have never measured: Scope 3.

Common Scope 3 mistakes

Counting the same emissions twice, for example including leased offices in both Scope 2 and Category 8. Mixing years, so the spend data and the emission factors do not match. Using spend-based factors forever instead of improving the biggest categories. Excluding categories without explanation. And reporting a single number with no record of methods, which makes the next year’s comparison meaningless.

If your company has a target with SBTi, these numbers also become your yearly progress report. If you would like help preparing a Scope 3 screening or a full inventory, see GHG inventory services.

Measuring Scope 3 is the first step towards a credible net zero target.

For a quick first number on Scopes 1 and 2, use our free small business carbon footprint calculator.