What Are Emission Factors? How Businesses Calculate Carbon Emissions

Aug 27
9 min read

When you first start measuring your organisation’s carbon footprint, you might already have much of the information you need.

You may know how much electricity your office uses, how many miles employees travel for work or how much fuel your company vehicles consume. If you run events, you might also have information about attendee journeys, freight, catering or waste.

What those numbers don't tell you on their own is how much greenhouse gas they represent - this is where emission factors come in.

Emission factors help turn everyday activity data into an estimate of greenhouse gas emissions. They're an important part of carbon measurement and are used across everything from business travel and energy use to waste and event transport.

Understanding how they work can make carbon reporting feel much less complicated, particularly if you are only just starting to measure your footprint.

What Are Emission Factors?

An emission factor is a value used to estimate the greenhouse gas emissions associated with a particular activity.

Put simply, it acts as the link between something your business can measure and the carbon emissions associated with it.

For example, you might know:

How many miles an employee travelled
How many litres of fuel a vehicle used
How many kWh of electricity your organisation purchased
How much waste was produced
How far event equipment was transported

An appropriate emission factor can then be applied to that activity data to calculate an estimate of the resulting emissions.

The UK Government describes its conversion factors in a similar way: they allow organisations to calculate emissions from activity data such as fuel use, purchased electricity and distance travelled.

How Do Emission Factors Work?

At its simplest, the calculation looks like this:

Activity Data × Emission Factor = Greenhouse Gas Emissions

Imagine an employee drives 100 miles for a business meeting. The 100 miles is your activity data.

You would then select the appropriate emission factor based on information such as the vehicle and fuel type. Applying that factor converts the journey data into an estimate of its greenhouse gas emissions.

The same basic principle can be applied across many different activities:

For electricity, your activity data might be kWh consumed.
For fuel, it could be litres used.
For waste, it could be kilograms or tonnes.
For business travel, it might be passenger kilometres or miles travelled.
For freight, you may have information about the distance, vehicle and weight of goods transported.

This is one reason collecting good carbon data matters. The more useful information you have about an activity, the easier it becomes to select an appropriate factor and build a more meaningful emissions estimate.

Why Are Emissions Usually Reported As CO2e?

Carbon footprints are often described in terms of “carbon”, but organisations can be responsible for several different greenhouse gases.

To make these easier to compare and combine, emissions are commonly expressed as carbon dioxide equivalent, or CO2e.

CO2e provides a common unit for representing the warming effect of different greenhouse gases.

That means an emission factor may help convert something you understand operationally, such as litres of fuel or miles travelled, into kg or tonnes of CO2e that can then form part of your carbon footprint.

For a business measuring hundreds or thousands of different activities, this creates a consistent way to bring different emissions sources together.

What Are The UK Government GHG Conversion Factors?

If you are measuring emissions from UK activities, you are likely to come across the UK Government greenhouse gas conversion factors.

You may also hear these referred to as GHG conversion factors, carbon conversion factors or DEFRA emission factors.

The UK Government publishes a new set each year for organisations calculating and reporting greenhouse gas emissions from UK activities.

The current 2026 factors were published on 11 June 2026 and can be used by UK organisations of all sizes, as well as international organisations reporting their UK operations.

The factors cover a wide range of activities and can support calculations across Scope 1, Scope 2 and Scope 3 emissions.

For businesses beginning their carbon reporting journey, they provide an established source of factors rather than requiring organisations to develop their own calculations from scratch.

Are DEFRA Emission Factors And UK Government Conversion Factors The Same Thing?

You'll often see people refer to DEFRA emission factors when discussing UK carbon reporting.

This terminology can be confusing because the UK Government's company reporting conversion factors are currently published by the Department for Energy Security and Net Zero, while Defra also publishes separate spend-based emissions multipliers.

These are not the same thing.

The UK Government's company reporting conversion factors are designed to calculate emissions using activity data such as fuel consumed, electricity purchased or distance travelled.

Defra's spend-based multipliers, meanwhile, can be used to estimate supply-chain emissions based on spending across different categories of goods and services. The government notes that spend-based methods may be useful when an organisation does not have enough information to use activity-based methods.

So, if you encounter the phrase “DEFRA emission factors”, it is worth checking exactly which dataset or methodology is being referred to rather than assuming all UK emission factors work in the same way.

What Activities Can Emission Factors Be Used For?

Emission factors can be applied across many areas of a business carbon footprint.

Energy

Electricity, fuels and other forms of energy are common sources of emissions data.

Your organisation may already have useful activity data in utility bills, meter readings, fuel invoices or energy management systems.

Business Travel

Travel calculations can use information such as transport method and distance travelled.

Different journeys can require different factors, which is why knowing whether someone travelled by car, train, plane or another form of transport is more useful than simply knowing that a journey took place.

Company Vehicles

If your organisation operates vehicles, fuel consumption, mileage and vehicle information can help calculate associated emissions.

Freight And Transport

Businesses may need to measure emissions associated with moving goods, materials or equipment.

This is also particularly relevant to events, where staging, production equipment, signage and other materials may travel considerable distances before reaching a venue.

Waste

Waste calculations can take account of information such as waste type, quantity and treatment method.

Events

Events bring many of these activities together in one place.

An event carbon footprint might include travel, accommodation, energy, freight, catering, production materials and waste, with different emission factors used across the relevant activities.

For organisations running events alongside their normal business operations, using a consistent carbon measurement approach can make it easier to understand both individual event footprints and the wider organisational picture.

Do All Activities Use The Same Emission Factor?

Not all activities use the same emission factors, and this is an important part of getting carbon calculations right.

Two activities that sound similar can have very different emissions profiles, for example travel.

Driving 100 miles in one type of vehicle will not necessarily create the same estimated emissions as driving the same distance in another. Likewise, travelling 100 miles by rail is not the same as travelling 100 miles by car.

The appropriate factor can depend on the information available and the activity being measured.

This is why more detailed carbon data can be useful. Instead of recording simply “employee travelled to Manchester”, information about the distance and mode of transport gives you much more to work with.

However, that doesn't mean you need perfect data before you can begin measuring.

Where detailed information isn't available, there may be broader factors or alternative calculation methods that allow organisations to estimate emissions and improve their data over time.

Do Emission Factors Change?

Emission factors can change as the underlying data, technologies and methodologies used to calculate them change.

The UK Government publishes updated conversion factors each year and provides accompanying methodology and major-changes documents. It specifically advises regular users to review what has changed to help maintain consistent and comparable reporting between years.

Electricity is a useful example of why factors can change over time.

The emissions associated with electricity depend partly on how that electricity is generated. As the mix of generation sources changes, the relevant conversion factors can change too.

Transport technology, fuel composition and improvements to the underlying evidence can also affect factors.

For organisations reporting emissions regularly, this makes it important to record which factors and reporting year were used rather than treating an emission factor as a permanent number.

Which Emission Factors Should Your Business Use?

There isn't one universal factor that every organisation should use for every carbon calculation.

The appropriate source depends on what you are measuring, where the activity occurred, the reporting methodology being followed and the information available.

For UK activities, the UK Government's greenhouse gas conversion factors are an important source to understand. The government recommends that new users read the general guidance and the specific guidance accompanying the relevant worksheets before applying them.

Businesses should also aim to be consistent and transparent about the factors and methods they use.

If your organisation changes its methodology or data source, understanding that change is important when comparing emissions between reporting periods.

What Happens When You Don't Have Detailed Activity Data?

Carbon measurement rarely begins with perfect information.

You might know how much was spent with a supplier but not have detailed information about the materials they used. You may know an employee travelled to an event but not have complete journey information.

There are different approaches available depending on the data you have.

For example, the UK Government distinguishes its activity-based company reporting conversion factors from Defra's spend-based multipliers. Spend-based approaches can provide an initial estimate of supply-chain emissions where sufficient activity data isn't available.

The important thing is to understand what your calculation is based on.

An estimate created from broad information should not be presented as though it has the same level of detail as a calculation built from specific activity data.

Instead, carbon measurement can improve over time as your organisation identifies data gaps and introduces better collection processes.

Why Emission Factors Matter For Carbon Reporting

Emission factors can sound like a highly technical part of carbon accounting, but their purpose is actually very practical.

Businesses already generate large amounts of operational data:

You have energy bills.
Employees book travel.
Vehicles record mileage.
Suppliers send invoices.
Events generate transport, catering and waste information.

Emission factors help translate this everyday information into carbon data that can be measured and understood.

Once that information has been converted into a consistent unit such as CO2e, organisations can start to see where their largest sources of emissions are, compare activity over time and identify areas where reductions may have the greatest impact.

This is why carbon reporting is not simply about producing a final number. The data underneath that number can help you understand what is actually happening across your organisation.

How Carbon Tracking Software Uses Emission Factors

If you've used a carbon calculator or carbon tracking platform, you may already have used emission factors without seeing the calculation happening behind the scenes.

Instead of manually finding a factor, checking its units and carrying out each calculation yourself, carbon software can help structure the process.

You provide the relevant activity data, such as energy use or travel information, and the platform can use appropriate factors to calculate the associated emissions.

For organisations managing many emissions sources, this can make carbon measurement much more manageable.

It also becomes particularly useful when you're tracking both business operations and events. Rather than keeping travel calculations in one spreadsheet, event emissions somewhere else and organisational data in another system, carbon tracking software can help bring those calculations into a more consistent process.

Using Emission Factors For Business And Event Carbon Tracking

At Scope, we help organisations turn their business and event activity data into carbon information they can actually use.

For business carbon tracking, that could mean measuring areas such as energy, travel and other operational activities.

For events, it could include attendee travel, venues, accommodation, freight, catering, production and waste.

Emission factors are part of the calculation process that allows this activity data to become measurable emissions.

Bringing business and event carbon tracking together also gives teams greater visibility over the information behind their footprint, rather than seeing carbon reporting as a single number produced at the end of the year.

Start With The Data You Already Have

You don't need to become an expert in emission factors before you can start measuring your carbon footprint, begin with the information your organisation already has.

Look at your energy bills, fuel records, travel information, supplier data and event activity. From there, you can identify which data can be converted into emissions, where information is missing and which areas need better data collection in future.

Emission factors provide the bridge between those everyday activities and your carbon footprint.

Once you understand that relationship, the carbon measurement process becomes much easier to follow: collect useful activity data, apply an appropriate emission factor and use the resulting emissions data to understand where your impact is coming from.

Scope helps businesses and event teams bring that process together in one platform, so you can measure emissions, improve your data and build a clearer picture of your carbon footprint over time.