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How does a small organisation work out its carbon footprint without buying software?

Three things are needed: activity data you already hold, the UK government's published emissions factors, and a spreadsheet. Multiply each activity by the factor for its category, record which year of factors was used, and total the result. For a small organisation that is a day or two of work.

What you are measuring

A carbon footprint is a sum of activities, each converted into kilograms of carbon dioxide equivalent. The Greenhouse Gas Protocol Corporate Standard sorts those activities into three groups, and the grouping matters only because it stops things being counted twice:

• Scope 1, fuel you burn yourself: a gas boiler, a van, a generator.
• Scope 2, electricity you buy.
• Scope 3, everything else you cause: goods and services you buy, staff commuting, business travel, waste, deliveries, etc.

Most small organisations find scope 3 is the bulk of the total and the part with the least data behind it.

The data is already in your filing

Activity	Where the number lives
Electricity, gas	Meter readings or annual bills, in kWh
Vehicle fuel	Fuel receipts in litres, or mileage records
Business travel	Expense claims: miles by mode, flights by route
Purchased goods and services	The purchase ledger, by spend category
Waste and water	Contractor invoices, in tonnes or cubic metres

Nothing there requires new measurement. It requires someone to read twelve months of paperwork once.

Where the conversion numbers come from

The UK government publishes greenhouse gas conversion factors for company reporting every year, free, as a spreadsheet. It gives kilograms of CO2 equivalent per kWh, per litre, per mile, per tonne and per passenger kilometre. Commercial carbon software uses the same public factors. You are paying for the interface, not the arithmetic.

Where you have no activity data, spend-based estimation is the fallback: apply an emissions factor per pound spent in a category. It is rough, and it must be labelled as an estimate rather than a measurement, but it is better than omitting a category and calling the total complete.

The spreadsheet

One row per activity, and these columns:

1. Activity description
2. Quantity and unit (4,120 kWh, 830 miles, £2,400)
3. Scope (1, 2 or 3)
4. Factor used, and the year of the factor set
5. Result in kg CO2e
6. Source of the quantity, so the figure can be checked a year later

Fix a base year and keep its factor set alongside the current one. Otherwise a reduction you report may be nothing more than the government revising a factor.

The three mistakes worth avoiding

• Double counting. Fuel bought for your own van is scope 1; a courier's diesel is scope 3. Counting both against the same journey inflates the total.
• Switching factor sets mid-series. Recalculate the base year rather than comparing two years measured with different factors.
• Presenting estimates as measurements. Mark every spend-based line as an estimate. An audit or a funder will ask, and the answer is easier if the spreadsheet already says so.

When software starts to earn its cost

A spreadsheet stops being adequate when several people enter data at once, when there are multiple sites or years to compare, or when a customer or funder requires a reporting format you have to produce repeatedly. That is a systems problem rather than a carbon problem, and it usually calls for a small custom tool rather than a subscription.

For EcoCounts, the community carbon footprint charity I founded, the collection system that tracked around 25 participating households month after month began as a spreadsheet, and the spreadsheet version is still in real use.

What it costs

Nothing but time, if you do it yourself: a day or two for the first year, less thereafter. If you would rather not, the same work done for you sits somewhere between a day and three days depending on how the purchase ledger is organised.