Measuring

Scope 1, 2 and 3 emissions in plain English

Almost every carbon footprint is split into three scopes. The first two are fairly easy to measure. The third is usually the largest, and the one most organisations leave out.

By Richard Harvie · Updated November 2026 · 6 minute read

In short

Scope 1 is what you burn, Scope 2 is the electricity you buy, and Scope 3 is everything your organisation causes elsewhere.
Scope 3 is usually the largest part of a footprint, and most of it comes from what you buy.
In year one, measure Scopes 1 and 2 and the Scope 3 sources you already have records for. Estimate your supply chain from spending the year after, and improve it over time.

The three scopes

The scopes come from the Greenhouse Gas Protocol, the method almost every organisation uses to measure its carbon. The UK Government's conversion factors use the same three groups.

Scope 1 covers direct emissions from things you own or control: gas burned in your boilers, diesel and petrol in your own vehicles, and refrigerant gases that leak from air conditioning.
Scope 2 covers the electricity you buy, along with any heat, steam or cooling. The emissions happen at the power station, but your use causes them.
Scope 3 covers everything else in your value chain. Upstream, that means what you buy, business travel, staff commuting and waste. Downstream, it means the use and disposal of anything you sell.

The same idea works at home. Your gas boiler and the family car are your Scope 1, and the electricity bill is your Scope 2. Everything else is Scope 3: the weekly shop, new clothes, the summer holiday flight and the lorry that collects your bins.

Why Scope 3 matters most

For most organisations, Scope 3 is where most of the emissions are. Among companies reporting to CDP, which runs the main global system for environmental disclosure, supply chain emissions average 26 times those from their own operations, yet companies are twice as likely to measure their operations as their supply chain. The public sector is no different. Research for the Scottish Government found that buying goods and services can account for more than 70% of a public body's emissions, but more than half of the bodies it surveyed did not yet calculate them.

There is a simple reason. Every van, laptop, meal and repair you pay for was made, grown or delivered by someone using energy and materials, and their emissions become part of your Scope 3. You cannot replace a contractor's boiler, but you can choose who you buy from, what you ask for and whether you need to buy at all.

The Scope 3 categories to look at first

The Greenhouse Gas Protocol splits Scope 3 into 15 categories, but not all of them will apply to you. Service organisations can usually set aside most of the downstream ones, which deal with products sold to customers. These are the ones most organisations should look at first.

Category	What it covers	Where to start
1. Purchased goods and services	Everything you buy, from paper to contracted services	Twelve months of spending by category
2. Capital goods	Vehicles, buildings, equipment and IT	Spending on major purchases
3. Fuel and energy-related	Electricity lost in the grid on its way to you	Your own kWh
4. Upstream transport	Deliveries you pay a courier or haulier for	Supplier data or spending
5. Waste	Waste and wastewater	Contractor reports and water bills
6. Business travel	Rail, air, hotels and staff using their own cars for work	Bookings and mileage claims
7. Employee commuting	Staff travel to work and, if you choose, working from home	A short staff travel survey
13. Downstream leased assets	Buildings you own and let to others, if you are a landlord	Energy Performance Certificates or tenants' energy data

A three-step way to measure it

Measure what you have. Business travel, waste, water and the electricity lost in the grid come from records you already hold, so include them from year one. The carbon calculator on this site covers the common ones.
Estimate the rest from spending. For what you buy, multiply what you spend in each category by an average emissions factor per pound. Defra publishes these factors, which it calls spend-based emissions multipliers. Use your spending without VAT, and bring it back to the price year the factors use, or inflation alone will make your emissions seem to grow. The calculator includes a rough supply chain estimate to show the scale.
Improve the data over time. A few big contracts usually make up most of the total, so start with your largest suppliers. Ask for their emissions and how much relates to your contracts, and use their figures as they become available.

Two warnings

A spend-based estimate is a map, not a measurement. Judging a supplier's emissions by what you pay it is like judging a car's fuel economy by its price: a fair guide across the market, and often well out for a single car. Every supplier in an industry gets the same factor, so switching to a cleaner one changes nothing, and paying more for a cleaner product makes the estimate go up. Use it to find where to look, not to track progress.

Do not count things twice. Energy bills, fuel cards, water, the waste contract and travel bookings all appear in your spending data, but they are already in your footprint. Take them out before you estimate the rest.

Finally, be open about what you have and have not included. Leaving out the supply chain is normal in year one; hiding the fact is not.

Sources

Rules and figures checked in November 2026. They change, so check the current version before you rely on them.