How to calculate an event's carbon footprint step by step

An event's carbon footprint is the total amount of greenhouse gases generated by staging it, from build to teardown and from venue energy to the journey of every person who attends. It is expressed in tonnes of CO₂e: CO₂ equivalent, a single unit that adds up CO₂ and the other greenhouse gases according to their warming potential.

Calculating it supports three concrete decisions:

• Comparing editions. With the same boundary and the same criteria, this year's footprint against last year's shows whether you have improved or only tried to.
• Reporting to sponsors, councils and partners. A figure documented with its method survives an awkward question. A general sentence about “sustainability” does not.
• Deciding where to act. Emissions are not evenly spread. Knowing which category weighs most stops you investing in the measure that sounds best rather than the one that reduces most.

An event footprint is neither a certification nor an audit. It is an inventory: a table of categories, data, factors and results that someone else could repeat. If a sponsor, an authority or a ticketing platform requires a specific format or verification, ask them what they need before you start, because what is required depends on who is asking.

The GHG Protocol divides emissions into three scopes according to who controls them: scope 1 covers direct emissions, scope 2 covers purchased electricity and scope 3 covers all other indirect emissions in the value chain. These are its official definitions and how they apply to an event:

There is a caveat about the audience. The GHG Protocol does not mention event attendees: its closest example is customers travelling to retail stores. Classing audience travel as scope 3 comes from the “Event Industry Scopes” scheme in Vision:2025, reproduced in the onboard:earth guide (2024), which places audience, crew and supplier, and artist travel in scope 3. The same guide adds that, even though it is scope 3, the organiser should do everything possible to influence those emissions through incentives, strategy and policy.

Before allocating sources to scopes, set your control criterion. A rented generator operated by your supplier can be scope 1 or scope 3 depending on whether you use operational or financial control. Which one you choose matters less than writing it down and applying it the same way every edition.

The calculation always follows the same logic: you define what you measure, collect activity data, multiply it by emission factors and document every decision. These are the nine steps, in the order in which it is best to take them:

1. 1

   Define the calculation boundary

   Decide which event, which days (build and teardown included) and which sources are in. Set the control criterion (operational or financial) and note what you leave out and why. A clear boundary is what makes two editions comparable.

2. 2

   Collect the activity data

   Gather the physical quantities by category: kWh, litres of fuel, kilos of waste, hotel nights, kilometres and transport mode. Note the source of each figure (invoice, supplier report, survey, estimate) and who provided it.

3. 3

   Choose the emission factors

   For each activity, pick a published factor for the year of the event from a recognised source. Use as few sources as possible and record which one you used, with its version and date.

4. 4

   Calculate by category

   Multiply each activity figure by its factor: emissions = activity data × emission factor. Do it category by category and scope by scope, not with a single overall total, so you can see what weighs most.

5. 5

   Add up and interpret

   Add the categories by scope and in total. Work out each one's percentage of the total and rank them from largest to smallest. That ranked list is the basis of your reduction plan.

6. 6

   Set the intensity

   Divide the total by attendance-days (attendees per day multiplied by event days) and, if you need to, by unique attendees. Intensity (kg CO₂e per attendance-day) lets you compare editions of different sizes.

7. 7

   Document the assumptions

   Record every assumption: average car occupancy, the distance assumed for people who did not answer the survey, the split of transport modes, the factor used. Without written assumptions, nobody can repeat or defend the calculation.

8. 8

   Compare with the previous edition

   Compare only on the same boundary and the same criteria. If you have changed factor source or method, recalculate the previous edition with the new criteria before comparing.

9. 9

   Set measurable targets

   Turn the result into concrete goals by category: for example, raise average occupancy per car or lower the intensity of audience transport. Define the indicator, the starting value and the review date.

You need one activity figure for each emission category, and most already exist in invoices, contracts and supplier records; audience transport is the exception, because it is almost never recorded. This table summarises what to ask for, from whom and how hard it is to get:

Start with the categories where the data is easy and ask for the rest well ahead. Send suppliers, before the event, a sheet with exactly what you need: units, period and format. Asking for invoices after teardown often means not receiving them.

An emission factor converts a quantity of activity (a kWh, a litre, a passenger-kilometre) into kilos of CO₂e, and its source and year shape the final result as much as the figure you measure. It must correspond to the year the event took place, because factors such as electricity change every year with the generation mix.

Where to find them in Spain:

• Official factors for the relevant year. For fuels and electricity in Spain, use the official emission factors published by the authorities, always for the year the event took place. Check which scopes each tool covers: if it does not include scope 3, it does not cover audience transport.
• Your electricity supplier's mix. The electricity factor depends on the supplier and the year; look it up on your invoice or ask your supplier.
• IDAE. Its conversion factor table gives emissions per passenger-kilometre for cars, buses, trains and other modes. Use it citing its stated purpose (MOVES programme projects) and the version you consulted.
• DEFRA (United Kingdom). The onboard:earth guide (2024) says these factors can be used across Europe although they are based on UK averages. If you choose them, record it as a limitation.

This table shows IDAE factors for some modes. It helps you see the order of magnitude and the importance of occupancy; it is not for copying values without reading the source:

The IDAE car factor (120.7 g per passenger-km) is calculated with 1.2 people per vehicle, which equals about 144.8 g per vehicle-km (120.7 × 1.2, a derived calculation). If the cars arriving at your event carry more people, the per-person factor falls almost in proportion: for the same car, 3 people would give about 48.3 g per passenger-km and 4 about 36.2 g (144.8 ÷ 3 and ÷ 4, simplifying that consumption does not depend on load). That is why real occupancy matters more than any factor.

At UK music festivals, audience travel is the largest category of the footprint: 64% of an average of 15.9 kg CO₂e per person per day, according to The Show Must Go On, Edition 3 (Vision for Sustainable Events, 2026). It is a figure for that country and that type of event, useful as a signal of where to look first and not as a number for yours.

The reason is scale. Thousands of people make a round trip to the same place at the same times, largely in cars with few occupants. At UK music festivals with camping between 2010 and 2014, the sector average was 2.6 passengers per car, according to the 2015 Powerful Thinking report, and the same report estimated that raising it to 3.5 would cut audience travel emissions by 20% for that set of festivals. As a general reference, the European Environment Agency cites average car occupancy of around 1.5 people (EEA, report 19/2020).

There is another reason it weighs on the result: it is the category you control least. The 2015 report stresses that audience travel is not strictly an operational emission and is not under the organiser's direct control. That is why it is measured less and reduced less, even though the 2026 report calculates that a 32% cut in audience travel emissions would reduce sector emissions by nearly 20%. The onboard:earth guide (2024) adds that the best results in encouraging sustainable travel come at the ticketing stage.

To estimate your audience's transport you need four pieces of data per group of attendees: where they come from, which mode they use, how many kilometres they travel (round trip) and, if they go by car, how many people are in each vehicle. Each group's emissions are people × kilometres × factor per passenger-kilometre and, for cars, factor per vehicle-kilometre divided by occupancy. Ticketing postcodes let you calculate straight-line distances, an approximation that understates the real route: say so in your assumptions. For the process in more detail, see the guide on attendee transport emissions.

When data is missing, estimate with an explicit method, calculate a range instead of a single number and document every assumption. A result with declared uncertainty is worth more than one that looks exact but nobody can reproduce.

For audience transport, the onboard:earth guide (2024) suggests combining several sources:

• Ticketing postcodes. Ask your ticketing platform for those of all tickets (or of parking passes) and calculate distances.
• Survey. Ask how each person arrived, from where and, if by car, how many were travelling. It can be done at the event or in a follow-up email.
• Volunteer counts. At the entrances, count how many people arrive on foot, by bike, by train or by car.
• Sales data. If you charge for parking or sell coach seats, ticketing already knows how many spaces and how many people there are.

Then work with ranges. Calculate a low, a central and a high scenario by changing only the most uncertain assumptions (typically average occupancy and the distance for people who did not answer). If the range between low and high is very wide, that category deserves better measurement next edition.

Label each category with the quality level of its data: measured (invoice, meter, record), estimated (sample or survey) or assumed (no data of your own). With that column, the report reader knows which parts are firm and which are a first approximation, and you know where to invest next edition to improve measurement.

A good footprint report fits in a table: categories, scope, emissions, percentage of the total and intensity per attendance-day. This is the structure, with hypothetical figures and no emission factors, so you can see how it reads:

The hardest figure to obtain for scope 3 is the real occupancy of the cars arriving at the event, and that is where organised carpooling provides measured information instead of assumptions. Without it, the calculation starts from a generic average occupancy and the whole category inherits the uncertainty.

To bring this data into your report, replace your occupancy and distance assumptions with the values measured on the shared trips and make clear in the data sheet which part of the audience is measured and which is estimated. CO₂ avoided is a reduction against the scenario in which each passenger would have travelled on their own by car. Present it as a separate indicator with its method, and do not subtract it from your gross total without explaining it.

If you do not yet have a plan for audience transport, the guide to sustainable event mobility summarises the options and how to combine them, and the one on shuttle buses vs carpooling helps you decide the role of each.

The most effective reductions come from acting first on the category that weighs most in your results table, and communicating them with the same method you used to measure them. This table links each category to common levers and to the indicator that shows the effect. To organise the transport measures in a working document, start from the event mobility plan.

When communicating, follow a few simple rules that protect your credibility:

• Publish the boundary and the method. Say what the calculation includes and excludes, and which sources the factors come from.
• Give totals and intensities together. A lower intensity with a higher total is an efficiency gain, not an absolute reduction, and it is worth saying so.
• Compare only with your own earlier editions, on the same criteria, not with events of a different size or format.
• Do not use other people's figures as if they were yours. The UK's 64% does not describe your festival.
• Separate reduction from offsetting. Report offsetting separately and do not present it as a reduction of your gross footprint. Avoid saying the event is “carbon neutral” unless you can back the method.
• Acknowledge uncertainty. A sentence such as “part of the transport data is estimated, within this range” builds more trust than a total with no caveats.

The most common failures concern the boundary and the data, not the formula. Check this list before accepting the calculation:

• Leaving out audience travel because it is hard to measure, when it is usually the heaviest category.
• Mixing factors from different sources or years without documenting it.
• Comparing editions on different boundaries and attributing the difference to a real improvement.
• Counting the same source twice, for example a generator in scope 1 and again as a supplier service in scope 3.
• Presenting estimates as measurements, without saying which part of the data is assumed.
• Waiting until the end to collect data. Surveys and counts are designed before the event; so are supplier invoices.
• Not saving the assumptions, so the next edition cannot repeat the calculation.

If audience transport is the category that weighs most in your footprint, VIB3S is the carpooling platform for events that we recommend for acting on it and measuring it. Attendees share a car with other people going to the same event from a free app (iOS and Android) or from a web widget that integrates into your website, ticketing or emails with a single line of code, with nothing to download to view and request trips.

VIB3S builds your event's community and has the widget ready in under 24 hours. The driver splits the real trip costs (fuel and tolls) with passengers, and VIB3S complements public transport and shuttles; it does not replace them. With the completed trips, you receive the data your scope 3 calculation needs:

• Geographic origin of the audience.
• Arrival and departure time slots.
• Trips with the highest demand.
• Average occupancy per vehicle.
• Shared kilometres and cars avoided.
• CO₂ avoided, calculated and validated over completed trips.