It’s common for event businesses to already hold one kind of carbon data: their spend. Invoices for catering, freight, stand builds and hotels can be turned into an emissions figure quickly by applying a carbon factor to every pound spent. That speed is why spend-based reporting is so common, and in some situations it is a reasonable place to start. The problem comes when it becomes the only method. A spend-based figure follows the budget, so it struggles to show the effect of the decisions that change an event’s footprint, such as a plant-based menu, a reused stand or a consolidated delivery. Activity-based measurement calculates emissions from what physically happened: kilowatt hours, kilograms, kilometres and meals served. For events, that is the data that makes carbon reporting credible and reduction decisions possible.
What’s the difference between spend-based and activity-based emissions?
Both methods use the same basic calculation: a quantity multiplied by an emissions factor. The difference is what that quantity measures.
- Spend-based: money spent multiplied by an emissions factor per pound (kgCO₂e per £). The factor is an average for a whole sector, built from economic data.
- Activity-based: a physical quantity multiplied by a factor for that specific activity. That could be kilowatt hours of electricity, litres of diesel, kilograms of timber, miles travelled or meals served by dietary type.
Take a delivery to the site. An activity-based calculation uses the vehicle type and the distance. For an average petrol car, 10 miles × 0.33875 kgCO₂e per mile gives 3.39 kgCO₂e. A spend-based calculation takes the invoice total and applies an average factor for transport services. The same £150 invoice could cover a cargo bike courier or a diesel van, and both would produce the same figure.
The GHG Protocol’s technical guidance for calculating Scope 3 emissions lists its calculation methods in order of how specific they are to what was bought. Spend-based sits at the bottom, as the method to use when the others are not feasible.
Why spend-based figures fall short for events
Event emissions are shaped by decisions: what is served, what is built and how it gets to site. A sector-average factor per pound cannot see any of those decisions. The examples below come from event teams measuring with activity data in TRACE.
Catering: the menu matters more than the bill
The University of Birmingham’s Venues & Events team chose to measure with activity data from the start. At the Royal Geographical Society’s annual conference, they recorded what was served, by meal and dietary type, along with the serveware used. That detail showed that lower-carbon menus and compostable serveware cut catering emissions by more than 82%, avoiding over 10 tonnes of CO₂e.
If the University of Birmingham had applied a spend-based method, it would show the same emissions per pound whatever is on the plate. A beef main and a plant-based main at a similar price would score the same, even though plant-based meals can produce up to 95% fewer emissions than red meat.
Production: reuse doesn’t show up in spend
At The Meetings Show, 96.6% of the materials used to build Lime Venue Portfolio’s stand were reclaimed or reused. TRACE counts reclaimed, reused and hired stock as zero embodied carbon, because those emissions were accounted for in the material’s first use.
Under a spend-based method, a hire fee still carries emissions per pound spent. A reused stand can look much the same as a new build, so the decision that made the biggest difference goes unrecorded.
Lower spend doesn’t always mean lower emissions
When Jack Morton designed the HERE Technologies booth at CES, the team compared material and transport options in TRACE before committing to a design. The final build cut both carbon and budget by 20%.
Because the carbon figure came from materials and logistics data, it reflects real changes to the build. A spend-based method would have reported the same 20% reduction for any 20% budget cut, whether or not anything physical changed. Spend-based estimates can also miss in the other direction: a University of Bayreuth study found spend-based figures overestimated a company’s footprint by 11%, because the spending categories were too broad.
Can you trust a year-on-year carbon reduction?
Only if you can explain where it came from. Two things can move an event’s carbon figure without anything changing on site: prices and emissions factors.
Prices only affect spend-based figures. Inflation, discounts or a cheaper supplier all change the result. Spend less and the footprint falls, even if the event used the same materials, power and menu.
Emissions factors affect every method, because they are updated each year. In 2026, UK grid electricity factors fell 26% as the grid decarbonised, while international rail factors rose 154% per passenger once pre-pandemic data was replaced.
With activity data, you can separate the two. The kilowatt hours, miles or meals underneath stay the same, so you can show which part of a change came from your decisions and which came from updated data.
Reporting a few non-carbon metrics alongside your footprint makes this straightforward:
- Energy use in kWh
- Number of journeys, total mileage and mode split
- Waste by weight and destination
- Meals served by dietary type
That way, when you report a reduction, you can show the working behind it.
When is spend-based data reasonable?
Spend-based data works for purchases that are numerous, low in impact and hard to measure physically. Our rule of thumb: use activity data wherever emissions are high and decisions get made, and use spend for the long tail.
That is how TRACE is built:
- Event measurement uses activity data in every module. Where actual figures are missing, TRACE estimates from physical benchmarks. Venue energy, for example, falls back from meter readings to a share of the venue’s annual usage, then to benchmarks based on floor area and days hired.
- Crew travel has no estimate option. That data sits within the organiser’s or contractor’s control, so TRACE asks for actual journeys.
- Business Operations uses spend for purchased goods and capital goods only, such as office supplies, software, furniture and professional services. Energy, fuel, logistics, travel, commuting and waste all use activity data.
Outside the events industry, organisations take a similar approach. The Premier League’s published emissions methodology, for example, prioritises activity data, uses spend-based data where activity data is not available, and reviews data quality each year to move from one to the other.
Whatever mix you use, record which method sits behind each figure. That way anyone reading your report can see how solid each number is.
How to move from spend-based to activity-based data
You don’t need to switch everything at once. Start where the emissions are largest and the data is easiest to get.
- Start where you have the most control and the data is easiest to get. Start with the emission sources you can influence. Across 954 events in 22 European countries, travel was the largest single contributor, but over 60% of emissions came from production, materials, catering and infrastructure. These areas sit within your control, and the activity data is usually easier to collect. Travel is much harder to influence, so keep measuring it, but put your first effort where your own decisions change the result.
- Use the activity data you already hold. Meter readings, fuel volumes from generator hire, delivery notes with weights and distances, catering orders by dish and registration data on how attendees travel are often collected already. They just aren’t being used for carbon.
- Ask suppliers for quantities. Build data requests into briefs and contracts: kWh, litres, kilograms, miles and meal numbers. Our guide to engaging your supply chain covers how to do this without slowing suppliers down.
- Estimate physically before estimating financially. If you can’t get an actual figure, a benchmark based on floor area, headcount or distance is still closer to what happened than a spend figure.
- Keep spend for the long tail. Office supplies, software and professional services can stay spend-based without weakening your reporting.
- Measure the same way every time. Consistent methods let you compare events and years, and show genuine progress.
Frequently asked questions
What is spend-based carbon accounting?
Spend-based carbon accounting estimates emissions by multiplying the money spent on a good or service by an average emissions factor for that sector, expressed as kgCO₂e per pound or other currency.
What is activity-based carbon accounting?
Activity-based carbon accounting calculates emissions from physical data, such as kilowatt hours, litres of fuel, kilograms of material, distance travelled or meals served, multiplied by a factor for that specific activity.
Which method is more accurate for event emissions?
Activity-based. Event emissions depend on choices such as menu, materials, reuse, transport mode and distance. Activity data captures those choices, while spend data only reflects what they cost.
Can you use both methods together?
Yes. Many organisations use activity data for their largest emission sources and spend-based estimates for smaller, lower-impact purchases.
Does TRACE use spend-based data?
TRACE uses activity data for all event measurement. In Business Operations, spend-based factors are used only for purchased goods and services and capital goods, such as office supplies, software and furniture.
Measure what happened
Spend data tells you what an event cost. Activity data tells you what it was made of, and that is what you need to reduce its footprint and report it with confidence.
TRACE measures events and business operations in one platform, with activity data built into every event module.
- Book a demo to see how TRACE captures activity data across your events.
- Download the Event Carbon Measurement Starter Pack for a step-by-step guide to getting started with event carbon measurement
- Explore more guides and tools in the event carbon measurement hub.
