Free options include online calculators, downloadable spreadsheets and collections of specialist calculation tools. The right starting point depends on your sites, activities, available data and the output someone is asking you to produce.
This comparison covers five options with publicly available provider information checked in November 2026. It is a desk review, not a hands-on product test or a ranking. Free access and included features can change, so confirm the provider's current terms before putting business data into a service.
In this guide
The shortlist
| Option | Format | Provider's intended starting point | Check before choosing |
|---|---|---|---|
| SME Climate Hub Small Business Carbon Calculator | Online calculator | Small businesses beginning measurement, particularly a single site | Activity coverage and the output your recipient needs |
| Murmurate through SME Climate Hub | Online calculator | More complex businesses, including multiple sites | Current access terms, data detail and sharing options |
| US EPA Simplified GHG Emissions Calculator | Downloadable Excel tool | Organisations beginning an annual inventory | Geography, relevant sources and spreadsheet requirements |
| GHG Protocol calculation tools | Collection of tools and guidance | Specific activities, sectors and inventory tasks | Which combination covers your boundary |
| Persefoni Pro | Online platform with a free tier | Lower-to-medium complexity footprint measurement | What the free tier includes versus paid reports or other additions |
These are not five equivalent products. Two are offered through the same hub, one is a spreadsheet and one is a modular toolkit. The comparison makes those differences explicit so a reader can choose a route rather than mistake a list position for a quality score.
1. SME Climate Hub Small Business Carbon Calculator
SME Climate Hub describes this calculator as a simple starting point for small businesses with one site. That makes it worth considering when you are organising a first measurement exercise.
Before starting, list the records you can supply and the information the customer or reporting recipient expects. Try to establish whether the output covers that request, rather than assuming that any total footprint will do.
2. Murmurate through SME Climate Hub
The same official comparison describes Murmurate, previously the Advanced Business Carbon Calculator, as a more comprehensive option with support for multiple sites. The hub identifies both calculators as free to use.
For a business with several locations, prepare a site list and a consistent reporting period before evaluating it. Check how the current service handles the inputs, calculations and exports you need. We have not tested those workflows in an account.
3. US EPA Simplified GHG Emissions Calculator
The EPA calculator is a free Excel tool for estimating an annual inventory from activity data. EPA describes small and medium organisations starting GHG management as its primary audience.
Its download page explains spreadsheet-version requirements and navigation macros. Review those requirements with your normal software and security process. A free workbook can still require time to collect data, understand boundaries and check which factors are suitable for your circumstances.
4. GHG Protocol calculation tools
The GHG Protocol collection includes tools for activities such as combustion and transport, with guidance for their use. Most companies need more than one tool to cover their emissions sources.
This route can suit a team willing to work through the relevant methods and assemble the outputs. Read the guidance before entering numbers. Check tool versions, units and boundaries when combining workings, and avoid counting the same activity twice.
5. Persefoni Pro
Persefoni's pricing page presents Pro as a free starting option for footprint measurement, with a separate Advanced offering. Its feature comparison also identifies additions and differences between plans.
Check the specific report, export, collaboration and methodology features you need against the current plan. “Free” should describe the included service accurately. It does not mean every reporting output or advanced feature is included. This article does not independently verify the provider's feature claims.
Choose with a small test case
Use fictional data first. Select one site and one simple activity, then ask whether you can understand the route from input to output. A small test is easier to inspect than a complete inventory entered before you know how the tool behaves.
| Question | What a useful answer looks like |
|---|---|
| What does the tool cover? | A clear list of activities, scopes and exclusions |
| Can we explain the calculation? | Identifiable method, factor source, unit and version |
| Can we retrieve our work? | An export or retained record that meets the actual handover need |
| Who can access the data? | Clear account permissions and current privacy information |
| What remains our responsibility? | Collection, boundary choices, review and unresolved estimates are explicit |
| What might cost extra? | The required features are checked against the current plan |
The text checklist is designed for recording those answers. It contains no automatic product score or affiliate ranking.
Keep the source records whatever you choose
A calculated result still needs supporting activity records and a documented method. Keep the original bills, logs and assumptions. Preserve the calculation version reviewed and the decision that follows it.
Our utility bill tracker and manufacturing collection checklist help organise some of those inputs. The emission-factor directory helps record a source choice when your workflow requires one.
Auditably is not included as a carbon calculator in this shortlist. Its role is evidence and review around prepared climate-reporting figures. If that is the next problem you need to solve, inspect the example below and check the product's scope before considering a subscription.
Prepared with AI assistance using the linked sources and original worked examples. Illustrative records are fictional. No customer results, independent specialist review or hands-on software testing are claimed.