For many businesses, calculating Scope 1 and Scope 2 emissions is relatively straightforward.

You can obtain electricity consumption from your meter or energy bills. You know how much gas you have used. Fuel purchases, company vehicles and other direct activities can usually be measured with reasonable accuracy.

Scope 3 can be very different.

A significant proportion of a business’s carbon footprint can sit outside its own buildings, vehicles and direct operations — within the products, materials and services it purchases from other organisations.

That creates a fundamental challenge:

How do you calculate the carbon footprint of something another business has produced for you?

The long-term answer is increasingly going to be:

Ask them.

And, importantly, make providing that information a normal part of doing business with your organisation.

Purchased goods and services can be a major part of Scope 3

Under the Greenhouse Gas Protocol, purchased goods and services form Scope 3 Category 1.

This covers the upstream, cradle-to-gate emissions associated with extracting, producing and transporting the goods and services purchased by the reporting company.

Depending on the nature of the business, this category can become one of the largest components of the entire organisational carbon footprint.

Think about what a typical business purchases:

• Raw materials
• Components
• Packaging
• Chemicals
• Office supplies
• IT equipment
• Cleaning services
• Maintenance
• Professional services
• Software and IT support
• Marketing
• Recruitment
• Contractors
• Machinery and equipment

Every one of these purchases has a carbon footprint.

The challenge is obtaining sufficiently good data to calculate it.

Spend-based carbon calculations are useful — but they should not necessarily be the destination

Where supplier-specific information is unavailable, businesses can estimate emissions using secondary carbon factors, including factors linked to expenditure or the materials contained within a purchased product.

CO2 Impact has been designed to accommodate different levels of information.

For purchased goods and services, users can select appropriate carbon factors, enter supplier-specific information where available, or use an estimated factor where better information cannot currently be obtained. The CO2 Impact methodology specifically encourages users to request a carbon footprint from the supplier, supported by documentation where possible.

This allows a business to get started.

You do not need perfect data before calculating your first carbon footprint.

But there is an important difference between:

estimating a supplier’s emissions, and

receiving carbon information relating to the actual product or service you purchased.

The GHG Protocol’s Scope 3 technical guidance recognises this hierarchy. More specific calculation methods will generally provide higher-quality Scope 3 information, although obtaining that information normally requires additional effort.

That means your first carbon footprint might legitimately rely heavily on estimates.

Your second and third should progressively become better.

Supplier engagement is one of the best ways of achieving that improvement.

Start with your key suppliers

Trying to obtain detailed carbon information from every supplier immediately can turn carbon reporting into an enormous procurement exercise.

It does not have to work like that.

A far more practical approach is to identify the suppliers responsible for the greatest proportion of your purchases or estimated emissions and start with them.

The GHG Protocol itself supports prioritisation. Its Scope 3 guidance recommends concentrating higher-quality data collection on the activities most significant to the company’s emissions, risks, opportunities and business objectives.

It even gives an example of a business concentrating supplier-specific data collection on a small number of suppliers responsible for the majority of purchased materials, while continuing to use secondary factors for smaller suppliers.

The same principle works well for SMEs.

You might begin with:

Your largest suppliers by annual expenditure

and then identify:

The products, services or materials likely to have the highest carbon impact.

Those two lists will often overlap.

You could initially approach your top 5, 10 or 20 suppliers rather than attempting to contact hundreds.

Over time, expand the programme.

Don’t just ask suppliers for their company carbon footprint

One of the most important distinctions when requesting supplier information is understanding exactly what you need.

A supplier might proudly tell you:

“Our company emitted 250 tonnes CO₂e last year.”

That information is useful.

But it does not automatically tell you the carbon footprint of what you purchased from them.

Ideally, you want the emissions associated with the actual:

product, material, component or service supplied to your business.

For example:

Manufacturer

Rather than simply providing its total company footprint, a manufacturer could provide:

Product A — 14.6 kgCO₂e per unit supplied.

Material supplier

A steel supplier might provide:

1.8 kgCO₂e per kg of the steel grade supplied.

Hotel

A hotel provider could provide:

18 kgCO₂e per occupied room night.

IT support company

A service business could provide:

6.2 kgCO₂e per support hour.

Maintenance contractor

The supplier might provide:

42 kgCO₂e per maintenance visit.

That immediately makes the information far more useful.

It connects carbon to the same units already used commercially to measure the transaction.

CO2 Impact supports this philosophy through carbon intensity metrics such as emissions per product, turnover, employee, client hour, site output and other operational measures.

Services need carbon footprints too

There can be a tendency to associate product carbon footprints with physical goods while treating services purely as financial transactions.

But services also have emissions.

An accountancy practice, engineering consultant, IT provider, recruitment business, cleaning contractor or marketing agency may have emissions associated with:

• Offices
• Electricity
• Heating
• Employee travel
• Business travel
• Homeworking
• IT equipment
• Cloud services
• Purchased goods and services
• Company vehicles
• Other operating activities

The question is how much of those emissions should reasonably be associated with the service provided to a particular customer.

CO2 Impact’s methodology allows service providers to allocate emissions using sensible operational measures such as contract value or staff hours. Where a supplier can provide a specific emissions figure for the service delivered, that value can be entered directly.

This creates an important opportunity.

Service businesses can begin reporting carbon in terms their customers understand:

kgCO₂e per consultancy day

kgCO₂e per customer visit

kgCO₂e per room night

kgCO₂e per employee placed

kgCO₂e per support hour

kgCO₂e per £1,000 of service delivered

Once that becomes common, carbon can start functioning like another business performance metric.

Make carbon information part of procurement

One of the biggest mistakes businesses can make is treating supplier carbon information as something requested once a year by the sustainability manager.

An email goes out.

Some suppliers reply.

Some ignore it.

Others send a sustainability report containing very little usable data.

Then the exercise starts again next year.

There is a better approach.

Move the carbon requirement into procurement.

If carbon information matters to your organisation, it should appear alongside your other supplier requirements.

That means incorporating it into:

• Supplier onboarding
• Requests for quotation
• Tender documents
• Purchase agreements
• Framework agreements
• Supplier reviews
• Procurement policies
• Purchase terms and conditions

The objective is to establish the expectation before the purchase is made.

Put the requirement in your purchasing terms and conditions

Businesses should consider including a specific requirement within their purchasing terms and conditions requiring suppliers to provide appropriate carbon information.

The exact wording should be reviewed to suit the company’s procurement and legal arrangements, but the principle could be along the following lines:

Example carbon reporting procurement condition

Environmental and Carbon Information

The Supplier shall, where reasonably available, provide information relating to the greenhouse gas emissions associated with the products or services supplied to the Customer.

Where practicable, carbon information should be provided at product or service level and expressed in an appropriate operational unit, for example kgCO₂e per product, kgCO₂e per kg of material, kgCO₂e per service hour, visit, transaction or other appropriate unit.

The Supplier should identify the methodology, reporting boundary, reporting period and principal data sources used in determining the carbon footprint.

Where product- or service-specific information is not currently available, the Supplier should provide relevant organisational carbon information and cooperate with reasonable requests from the Customer to improve the quality of emissions information over time.

Supporting evidence should be made available where reasonably practicable.

This does something important.

It changes the conversation from:

“Would you mind completing our carbon questionnaire?”

to:

“Providing carbon information is one of our standard supplier requirements.”

That is a significant difference.

CO2 Impact’s own methodologies adopt the same principle in other areas of Scope 3 reporting. For example, its downstream leased asset methodology recommends putting emissions data requirements directly into contractual arrangements with lessees.

Carbon data requirements can increasingly become part of normal commercial contracts.

Do not make the requirement impossible on day one

There is also a danger.

A large customer could simply write:

“All suppliers must provide verified product carbon footprints.”

That sounds ambitious.

But for many smaller suppliers it may be completely unrealistic.

They may never have calculated their organisational footprint, never mind performed a detailed life-cycle assessment for every product.

The result could be poor data, arbitrary estimates or smaller suppliers being excluded from contracts simply because they do not have a sustainability department.

Supplier engagement should therefore combine expectation with support.

A sensible procurement policy might establish progressive levels of carbon data maturity.

For example:

Level 1 — Starting

Supplier provides basic operational information or acknowledges that carbon reporting is being developed.

Level 2 — Organisational footprint

Supplier calculates Scope 1, Scope 2 and relevant Scope 3 emissions.

Level 3 — Carbon intensity

Supplier establishes useful metrics such as emissions per tonne, product, hour, employee or £ turnover.

Level 4 — Product or service carbon information

Supplier provides emissions specifically associated with products or services supplied.

Level 5 — Improved assurance

Methodology, boundaries and supporting evidence are increasingly documented and, where appropriate, independently reviewed.

The important thing is movement.

Your supplier does not necessarily need to have Level 5 information tomorrow.

But you should increasingly expect them to be moving in that direction.

Help important suppliers calculate their footprint

For some key suppliers, simply demanding data may not be the best way to obtain it.

Helping them create the information may achieve far more.

This is particularly relevant where a supplier is strategically important but relatively small.

You might depend heavily on a specialist manufacturer, contractor or service provider that has excellent technical capabilities but very limited carbon reporting experience.

Instead of repeatedly requesting information they cannot provide, consider helping them get started.

Give selected suppliers CO2 Impact free for their first year

One practical approach could be to provide strategically important suppliers with access to CO2 Impact free for their first year.

The message to the supplier becomes:

“We are increasingly measuring carbon through our supply chain and will need better information from our suppliers. Rather than simply asking you for data you may not currently have, we want to help you calculate it.”

That is a very different supplier relationship.

The supplier gets a practical tool for managing its own carbon footprint.

You get progressively better Scope 3 information.

And both businesses begin working from a common carbon-accounting structure.

The supplier can start by calculating its own business footprint, understanding its emissions sources and building a Carbon Reduction Plan.

As its data improves, it can then begin calculating meaningful carbon intensity metrics or carbon footprints for the specific products and services it supplies.

That information can subsequently feed into your own carbon reporting.

You are improving the supplier — not merely collecting data

This is an important mindset.

Supplier engagement should not just be a data collection exercise.

It can become a supply-chain improvement programme.

Your suppliers calculate their emissions.

They identify energy reduction projects.

They improve material efficiency.

They examine transport.

They reduce waste.

They engage their own suppliers.

Their emissions fall.

And because their products and services form part of your Scope 3 emissions, those improvements eventually flow through into your carbon footprint as well.

That is how genuine Scope 3 reduction occurs.

Not by changing the spreadsheet.

By changing the supply chain.

Carbon information can eventually influence purchasing decisions

Once consistent supplier carbon information becomes available, businesses can start incorporating emissions into procurement decisions.

Historically, a buyer may have compared:

Price

Quality

Delivery

Availability

Technical specification

Warranty

Service

Increasingly another measure can be added:

Carbon

Imagine two suppliers offering technically equivalent components.

Supplier A:

£95 per component
18 kgCO₂e per component

Supplier B:

£97 per component
11 kgCO₂e per component

Carbon is no longer an abstract corporate figure.

It becomes another piece of purchasing information.

That does not mean the lowest-carbon supplier automatically wins.

Commercial purchasing decisions are rarely based on a single criterion.

But carbon can now be considered alongside price, quality, delivery, risk and performance.

And that is when carbon reporting begins to influence real business decisions.

Measure suppliers against themselves as well as each other

Absolute comparison between suppliers can be difficult.

Different companies may currently use different calculation boundaries, assumptions and methodologies.

Initially, one of the most useful measures may therefore be improvement over time.

If a supplier reports:

2026 — 18.0 kgCO₂e per unit
2027 — 16.7 kgCO₂e per unit
2028 — 14.9 kgCO₂e per unit

you can see something meaningful happening.

The supplier is improving.

Carbon intensity metrics are particularly useful here because they account for changes in business activity. CO2 Impact’s methodology specifically identifies intensity measures as a way of tracking carbon efficiency over time while accounting for business growth or operational change.

That avoids one of the common problems with carbon reporting.

A supplier might grow its production by 30% and consequently increase absolute emissions by 10%.

At first glance, emissions have increased.

But emissions per product may have fallen significantly.

Both figures matter.

The intensity measure explains what is happening operationally.

Retain the evidence

Whenever supplier-specific carbon data is used, keep the supporting information.

CO2 Impact’s Purchased Goods and Services methodology recommends retaining documentation supporting supplier-specific carbon factors and periodically reviewing those factors as supplier reporting improves.

That might include:

• Supplier carbon footprint reports
• Product carbon footprint declarations
• Calculation methodologies
• Environmental Product Declarations
• Emails confirming supplied figures
• Reporting periods
• Units
• Data boundaries
• Verification statements
• Certificates
• Relevant assumptions

This becomes increasingly important as carbon information starts appearing in customer reports, tenders and procurement decisions.

The objective should always be traceability.

If someone asks:

“Where did this carbon figure come from?”

you should be able to answer.

Create a carbon data improvement programme

Businesses do not have to solve their entire supply-chain footprint in one year.

A practical programme could look like this:

Year 1 — Calculate

Complete the first organisational carbon footprint.

Use the best available data.

Identify purchased goods and services that are significant emissions sources.

Rank suppliers by expenditure and estimated carbon impact.

Year 2 — Engage

Contact priority suppliers.

Request organisational and product/service carbon information.

Add carbon data requirements to supplier onboarding and purchasing terms.

Help strategically important suppliers that currently cannot provide data.

Consider providing selected suppliers with CO2 Impact for their first year.

Year 3 — Improve

Replace estimated carbon factors with supplier-specific information.

Request carbon intensity measures.

Begin comparing supplier carbon performance.

Include carbon performance within supplier reviews and tender assessments.

Year 4 onwards — Reduce

Work collaboratively with suppliers on reduction opportunities.

Set procurement-related carbon reduction objectives.

Track changes in the carbon intensity of purchased products and services.

Increase the percentage of procurement expenditure supported by supplier-specific carbon information.

This creates something extremely valuable:

a measurable improvement in the quality of your carbon footprint itself.

Make supplier carbon data a KPI

One useful metric for procurement teams could simply be:

Percentage of purchasing spend covered by supplier-specific carbon data.

For example:

2026 — 12%
2027 — 35%
2028 — 58%
2029 — 76%

Another could be:

Percentage of strategic suppliers with a current carbon footprint.

Or:

Percentage of purchased products with a product-specific carbon factor.

These are understandable, measurable targets.

And importantly, they give procurement teams something they can actively influence.

Your customers may soon ask the same questions of you

There is another reason to get this right.

While you are asking suppliers for carbon information, your customers may be asking exactly the same questions about your business.

What is your carbon footprint?

What are you doing to reduce it?

What is the carbon footprint of the product we purchase from you?

Can you provide emissions per unit?

Can you provide carbon information for our Scope 3 reporting?

Can you provide evidence?

The supply chain works in both directions.

A business that develops this capability is therefore not simply improving compliance or sustainability reporting.

It may be improving its ability to win and retain business.

CO2 Impact can help both sides of the supply chain

CO2 Impact has been developed to turn operational business information into structured carbon information.

Businesses can use the platform to calculate and track their Scope 1, Scope 2 and Scope 3 emissions, manage suppliers, identify carbon reduction opportunities and progressively improve the quality of their emissions data.

The platform’s functional design links suppliers to business expenditure and enables reporting of purchases and their associated carbon impact by supplier.

It also supports allocating upstream supplier emissions to the products and services ultimately sold by the reporting business.

That becomes particularly powerful when both purchaser and supplier are improving their carbon data.

Instead of one business estimating another business’s emissions indefinitely, carbon information can progressively move through the supply chain.

Supplier → Product or service → Customer → Customer’s Scope 3 footprint

That is where carbon accounting ultimately needs to go.

Start asking the question

You do not need every supplier to have a perfect product carbon footprint today.

But businesses should start creating the expectation.

Ask your suppliers:

Do you currently calculate your carbon footprint?

Can you provide the carbon footprint of the product or service you supply to us?

What methodology have you used?

Can you provide supporting information?

If you cannot provide this today, when do you expect to be able to?

Then make the requirement part of future purchasing terms.

For your most important suppliers, consider going further.

Rather than only asking them for carbon data, help them create it.

Providing a key supplier with CO2 Impact free for its first year could be a relatively small investment in your own supply-chain carbon data.

They gain a carbon management platform.

You gain a supplier capable of providing increasingly useful carbon information.

Both organisations gain a clearer understanding of where emissions occur and where reductions can be made.

Carbon reporting becomes far more powerful when the whole supply chain participates

Scope 3 cannot ultimately be solved by one business sitting alone with a spreadsheet.

Every estimate represents information that potentially exists somewhere else in the supply chain.

The manufacturer knows how the product was made.

The haulier knows what transported it.

The contractor knows what resources were required.

The service provider knows how many hours were delivered.

The waste company knows how the material was treated.

Your challenge is connecting that information.

Start with estimates where necessary.

Identify the suppliers that matter.

Ask for better information.

Put carbon reporting into your purchasing requirements.

Help strategically important suppliers develop their own carbon reporting capability.

And progressively replace assumptions with real supply-chain data.

That is how a carbon footprint moves from being an annual reporting exercise to becoming a practical tool for managing the environmental performance of the business and its supply chain.

CO2 Impact — measure it, understand it, reduce it.