If you run a small business in the UK, you have probably heard that you should be measuring your carbon footprint. But where do you actually start? The whole thing can feel overwhelming. Scopes, emission factors, conversion tables. Most guides assume you already know what you are doing.
This one does not. Let's walk through it together, from scratch.
What Is a Carbon Footprint, Really?
Your carbon footprint is the total amount of greenhouse gases your business produces, measured in tonnes of carbon dioxide equivalent (tCO2e). That "equivalent" part matters because it means we convert the warming effect of different gases (methane, nitrous oxide, refrigerants) into CO2 terms so everything can be compared on the same scale.
For most UK SMEs, your footprint comes from three broad areas:
- The energy you burn directly. Gas boilers, company vehicles, generators.
- The electricity you buy from the grid.
- Everything else in your supply chain. Business travel, commuting, the things you purchase.
These three areas map to Scope 1, 2, and 3 of the GHG Protocol, the global standard for carbon accounting.
What Data Do You Need?
Before you start calculating, you need to gather some documents. Do not worry about getting everything perfect on your first attempt. Start with what you have and improve over time.
For Scope 1 (direct emissions):
- Natural gas bills (look for kWh consumed, not just the cost)
- Heating oil invoices (litres purchased)
- Company vehicle fuel receipts or mileage logs
- Refrigerant top-up records (if you have air conditioning or cold storage)
For Scope 2 (purchased electricity):
- Electricity bills (kWh consumed and your supplier name)
- District heating invoices, if applicable
For Scope 3 (indirect emissions):
- Flight bookings (origin, destination, class of travel)
- Rail tickets
- Hotel invoices (number of nights, country)
- Employee commuting data (a simple survey works)
- Major purchased goods and services (spend data or quantities)
Top tip: Pull together 12 months of data for a complete picture. Your financial year is usually the easiest period to use, since the records already exist.
The Calculation: Step by Step
Carbon footprint calculations follow a simple formula:
Activity data x Emission factor = Emissions (kgCO2e)
Activity data is what you collected above: the kWh of gas, the litres of fuel, the kilometres flown. Emission factors are published conversion rates that tell you how much CO2e each unit of activity produces.
In the UK, the standard emission factors are published annually by the Department for Energy Security and Net Zero (DESNZ). These are free to download and are the same factors used by large companies for their SECR reporting.
Here is how it works in practice:
- Gather your activity data for the reporting period (12 months)
- Match each activity to the correct emission factor from the DESNZ tables
- Multiply activity data by the emission factor
- Sum up all the results to get your total footprint in tCO2e
For example, if your office used 15,000 kWh of natural gas in a year, and the DESNZ emission factor for natural gas is 0.183 kgCO2e per kWh, your Scope 1 gas emissions would be:
15,000 x 0.183 = 2,745 kgCO2e (or about 2.7 tCO2e)
How Long Does This Take?
For a typical small office-based business doing this for the first time, expect to spend:
- 1 to 2 hours gathering bills and records
- 1 to 2 hours entering data and running calculations
- 30 minutes reviewing the results
So roughly half a day for your first measurement. It gets faster each year because you will know where to find everything.
Common Mistakes to Avoid
Using cost instead of consumption. Your gas bill shows both pounds and kWh. Always use kWh, because costs fluctuate with energy prices and do not reflect actual emissions.
Forgetting Scope 3. For most SMEs, Scope 3 (travel, commuting, purchased goods) is actually the biggest slice. Leaving it out gives you an incomplete picture.
Picking the wrong emission factors. Use the UK DESNZ factors for the correct year. Using American EPA factors or outdated UK figures will throw your numbers off.
Not setting a base year. Your first measurement becomes your baseline. Future reductions are measured against it, so document your methodology clearly so you can be consistent.
What Happens Next?
Once you have your baseline footprint, you can:
- Identify your biggest emission sources (your "hotspots")
- Set reduction targets, ideally aligned with science-based targets
- Start making changes, beginning with the quickest wins
- Track progress year on year
If you supply goods or services to the UK government, you may also need a formal Carbon Reduction Plan to comply with PPN 06/21.
Choosing the right tools matters here too. We wrote about how we approach technology decisions as a social enterprise, and the same principles apply to picking carbon accounting software. Look for transparency, data privacy, and tools that work for your context rather than against it.
ROOTED can walk you through this entire process step by step, entirely on your machine, with no data uploaded anywhere. We are running our first pilot with a small group of UK SMEs in August 2026, so if you would like to try it for yourself, head over to the ROOTED page to find out more and register your interest.
References
- GHG Protocol, Corporate Accounting and Reporting Standard (Revised Edition), World Resources Institute & WBCSD. ghgprotocol.org/corporate-standard
- UK DESNZ, UK Government GHG Conversion Factors for Company Reporting 2025. gov.uk/government/publications/greenhouse-gas-reporting-conversion-factors-2025
- Carbon Trust, SME Carbon Footprint Calculator. carbontrust.com/our-work-and-impact/guides-reports-and-tools/sme-carbon-footprint-calculator
- SME Climate Hub, Carbon Footprint Calculators for Small Businesses. businessclimatehub.uk/carbon-footprint-calculators
- DEFRA, Environmental Reporting Guidelines: Including Streamlined Energy and Carbon Reporting Guidance (March 2019). gov.uk/government/publications/environmental-reporting-guidelines-including-mandatory-greenhouse-gas-emissions-reporting-guidance