How to Calculate Your Business Carbon Footprint: A Worked UK Example with 2025 and 2026 Factors

Most guides to this topic list the same five steps and stop there. This one works through a full example with real numbers, using the UK Government’s published conversion factors, so you can check every line. It is written for small and medium firms, the ones now asked for a footprint by a large customer, a bank, a tender or an assessor. If you want the answer first, our free small business carbon footprint calculator does the Scope 1 and 2 sums for you.

What you need before you start

Pick one 12-month period and use it for everything. Your financial year is usually easiest, because the bills and accounts already line up.

Step 1: draw the boundary

For a small business the boundary is normally simple: every site and vehicle you own or control. If you rent an office and pay the energy bills, those emissions are yours. If energy is included in your rent and you cannot get the figures, note it and use a floor-area estimate rather than leaving it out.

Step 2: choose the right emission factors

An emission factor converts an amount of activity into kg of CO₂e. In the UK, almost everyone uses the Government’s greenhouse gas conversion factors, published each June by the Department for Energy Security and Net Zero. The 2026 set was first published on 11 June 2026 and covers activity in 2026. The rule is simple: use the set for the year your activity falls in. For a financial year that spans two calendar years, use the set for the year that most of it falls in, and keep the same rule every year.

Outside the UK, the method is the same but the electricity factor changes a lot by country, because it depends on how each grid generates power. Use your national factor or, better, your supplier’s own figure. Our calculator includes average grid intensity for many countries, from Norway and Sweden at well under 50 g CO₂e per kWh to coal-heavy grids at several times the UK figure.

Step 3: a worked example

Here is an example firm we made up to show the method: a 12-person office business with one diesel van, reporting for the 2025 calendar year. The amounts are illustrative; the factors are the real 2025 UK Government values.

Two points from the example. First, Scope 1 (12.46 t) is bigger than Scope 2 (5.31 t), which is common for firms that heat with gas or run vans. That tells you where reductions will count most. Second, the electricity line is “location-based”: the UK grid average. If you buy electricity on a renewable tariff, the GHG Protocol asks you to report a second, “market-based” figure using your supplier’s factor, alongside the location-based one.

The factor trap: a fall that isn’t a reduction

Now run the same firm through 2026 with exactly the same electricity use. At the 2026 factor, 30,000 kWh comes to 3,929 kg instead of 5,310 kg: a fall of about 26%, with nothing changed in the office. The 2026 set uses a new method with more recent grid data, which cuts the time lag in the electricity figures from two years to one. When you compare years, show the change from the factor separately from any change in what you actually used, or customers and assessors may read it as a reduction you made. Do not go back and recalculate earlier years with the new factors, unless you are correcting an error or your business has changed a lot, for example after an acquisition.

A footprint that falls because the government updated a factor has not fallen. Report the change in kWh and litres, not just the tonnes.

Step 4: screen your Scope 3

For most small businesses, Scope 3 is the largest part of the footprint: the goods and services you buy, business travel, staff commuting, couriers and waste. You do not need perfect data to start. A spend-based estimate multiplies what you spent in each category by an average factor for that kind of purchase, and shows you which categories matter. Then you collect better data only for the biggest two or three. The free GHG inventory template for Excel has a 15-category Scope 3 screening, and Scope 3 emissions explained describes each category with small-business examples.

Step 5: check it, write it down, sign it off

Before you share the number, check the obvious things. Gas in kWh, not cubic metres. Each bill counted once. Fuel-card litres, not pounds spent. Refrigerant top-ups included. And the same factor year used for every line. Then write a one-page note: the period, the boundary, the data sources, the factor set, and anything you estimated. That note is what makes the number believable to a customer, and it saves you hours when you repeat the exercise next year.

What to do with your footprint

The first footprint becomes your baseline: the year you measure progress from. What happens next depends on who asked for it. A large customer’s supplier questionnaire usually wants Scope 1, 2 and the Scope 3 categories you can estimate. A UK public tender asks for a Carbon Reduction Plan, and NHS tenders change on 1 April 2027 (see the 2027 NHS requirements). A bank or an EU customer may ask for the VSME standard, where the footprint goes into disclosure B3. Each uses the same numbers, so measuring once, carefully, pays off several times.

If you would rather hand it over, we prepare GHG inventories for small firms with documented factors and a base year, and the GHG Inventory Pro Workbook does the full Scope 1, 2 and 3 calculation in Excel if you prefer to keep it in-house.