Every delegate at your last event saw the same small card. It sat folded on the bed, asking them to hang up their towel if they were happy to use it again. It is the most recognised sustainability gesture in hospitality, and a large part of the reason event accommodation emissions get described rather than measured.
Then a sponsor asks what your event’s accommodation footprint was. Nothing about that card produces an answer. It is not a quantity, it has no unit, and it cannot go in a row of a report.
The card is a visible action. The accommodation line needs a measured one. Most event footprints lose a category in the distance between the two.
How event accommodation emissions are actually calculated
Event accommodation emissions are calculated by multiplying delegate room nights by an emissions factor per room night. The strongest factor comes from the hotel’s own measured data, the next best from a published benchmark for that country, and the weakest from money spent. The room nights themselves have to be captured while registration is open.
That is a hierarchy of evidence quality, not a menu. Supplier-specific data is the property’s own figure, calculated from its actual energy consumption. A published benchmark factor applies a regional or national average to your room-night count. A spend-based factor applies an intensity figure to what you paid, which is the fastest route and the least accurate.
Where you land on that hierarchy is barely a methodology decision; it is decided by what you asked the hotel for, and when. Teams that put the question in the contract get supplier data. Teams that remember after the event get an average.
One concession first. Accommodation is usually not the largest line in an event footprint; attendee travel generally is. The argument is not that hotel nights dominate your total, but that they are unusually easy to measure badly and easy to lose entirely.
What a hotel night’s footprint is actually made of
Reusing your towel reduces laundry, a genuine operational saving for the hotel. It is not what determines the carbon figure attached to your room night.
The hospitality industry already has a shared method for this. The Hotel Carbon Measurement Initiative (HCMI) was created in June 2012 by the Sustainable Hospitality Alliance and the World Travel and Tourism Council, working with 23 global hospitality companies, and reviewed by the World Resources Institute. Over 30,000 hotels now use it: this is the industry’s own methodology, not a framework imposed from outside.
HCMI calculates a hotel’s carbon footprint per occupied room on a daily basis. What goes into that calculation is worth reading closely. In the Alliance’s own words, HCMI:
“includes all energy used ‘on site’ (including fuels such as natural gas, oil and other fuels, purchased electricity, and mobile fuels from vehicles and other equipment) and emissions from refrigerants. It also includes, if applicable, carbon emissions from outsourced operations (e.g. laundry).”
Read the ordering again. A room night’s measured footprint is built from the energy it takes to run the building, plus refrigerants. Laundry appears last, as a conditional, and only when it is outsourced.
The towel card addresses a real cost sitting at the edge of the quantity you are asked to report. It is neither worthless nor a fraud. It simply answers a different question than your sponsor asked, the same gap that shows up in catering, where visible choices and measured impact are not the same set of things.
Are hotel stays included in Scope 3?
Partly, and less cleanly than most event teams expect. The category exists, but it was not written with your delegates in mind.
The GHG Protocol Corporate Value Chain (Scope 3) Standard sorts value chain emissions into fifteen categories. Category 6, Business travel, covers emissions from the transportation of employees for business-related activities in vehicles owned or operated by third parties.
Two words there create the problem. The first is employees. The people sleeping in hotel rooms because of your event mostly are not your employees; they are delegates, speakers, sponsors and contractors.
The second is transportation. Category 6 is built around getting people to places, and a bed is not a mode of transport.
An event organiser reading the standard does not find their own situation in it. The accommodation boundary is a decision you make, not one you look up. Decide it before the event opens, write it down, and apply the same rule across the portfolio. A boundary that moves between events produces a trend line that means nothing.
Room block or self-booked: the line that decides what you can report
This distinction determines whether you will have any data at all, and it has nothing to do with methodology.
Block nights are contracted and invoiced. Somebody negotiated a rate and signed for a number of rooms, so a document exists with quantities on it. Those nights survive reconstruction long after the event closes, because paperwork outlives memory.
Self-booked delegate nights leave no trace you hold. Nobody sends the organiser a bill for a room they did not book. If a delegate booked their own hotel, the only parties who know how many nights they stayed are the delegate and a company you have no relationship with.
That puts accommodation in an awkward middle position: not like energy or waste, which arrive as invoices with quantities already on them, and not as irrecoverable as attendee travel, since your room block gives you a real floor. The share of your room nights that is self-booked is the share of your accommodation line with a collection deadline, and that deadline is registration, not reporting season. It is the same timing problem that makes attendee travel the line item you cannot rebuild afterwards.
Where your event accommodation emissions factor comes from
When the hotel gives you nothing, you fall back on a published benchmark. It is a legitimate answer and a weaker one, and it is worth being honest about which you are using.
The Cornell Hotel Sustainability Benchmarking Index (CHSB) is the main reference point, drawing on more than 31,500 member hotels across 1,022 geographies covering 94 countries, and running annually since 2013. Its published datasets are the closest thing the sector has to an open benchmark.
CHSB is explicit about this. Among the stakeholder uses it lists is business travel, described as using the dataset to “estimate emissions of hotel stays for Scope 3 reporting”. You are not misusing a hotel-industry dataset by applying it to your event; you are using it as intended.
National factor sets are the other route. The UK government publishes annual conversion factors for company reporting, activity-based and covering Scope 1, 2 and 3, alongside a methodology report. The collection was last updated on 11 June 2026, with the 2026 factors published on 31 July 2026.
None of this changes the underlying point: a benchmark is what you use when you did not ask. Put the request in the hotel RFP and you get the property’s own measured figure instead of a national average, the difference between a defensible number and a plausible one.
The meeting space you are probably counting twice
A second HCMI output gets missed routinely. Alongside the footprint per occupied room, the methodology calculates a hotel’s carbon footprint per area of meeting space on an hourly basis.
Those are two separate measured quantities, and the distinction matters most in the case events hit constantly: the conference is held in the same hotel the delegates sleep in. Treated as one line, you either count the venue twice, once in the room nights and again in the function space, or you quietly drop the meeting space altogether.
The property can produce both, because its own methodology already separates them. Ask for both, and state which applies to what. Few event teams do, which is why accommodation and venue rows so often fail to reconcile.
What to ask for, and when
Almost all of the work behind credible event accommodation emissions sits upstream of the report, which is why it gets missed. The tasks are small and the deadlines are early.
- Put the emissions data request in the hotel RFP, not a post-event email. Ask for the property’s HCMI figure per occupied room night, and its meeting-space figure if you are using function space.
- Capture room nights and city at registration, for self-booked delegates as well as block bookings. One required field closes most of the gap.
- Decide the delegate boundary before registration opens and record it in writing.
- Decide the non-response treatment in advance, not when the deadline has passed and the call is made under pressure.
- Record which factor source you used for each event, so the number can be rebuilt and defended a year later.
None of these are technically demanding. Every one of them expires.
The row, not the gesture
The card on the bed deserves its due. It saves water, energy and cost on the hotel’s side of the ledger, and asks something reasonable of the reader. It is simply not what you were asked for.
What a sponsor, client or auditor wants in the accommodation row is a room-night count, a factor with a named source, and a boundary you can explain. Visible actions build trust with the people in the room. Measured actions survive review.
EventZero captures accommodation as structured activity data alongside travel, catering, production and logistics, so reporting becomes an aggregation rather than a reconstruction. There is more on carbon measurement and methodology for events across the rest of this category.
If you have an event with a room block still to be contracted, that is the point of maximum leverage on your eventual number. Book Your Carbon Strategy Session and we will settle the delegate boundary and the RFP wording before the contract is signed.
Frequently asked questions
- How do you calculate accommodation emissions for an event?
- Multiply delegate room nights by an emissions factor per room night. The strongest factor comes from the hotel's own measured data, the next best from a published benchmark for that country, and the weakest from money spent. The room nights themselves have to be captured while registration is open.
- Are hotel stays included in Scope 3?
- Partly, and less cleanly than most event teams expect. Category 6 of the GHG Protocol Scope 3 Standard covers business travel, defined as the transportation of employees in vehicles owned or operated by third parties. Event delegates are mostly not your employees, and a bed is not a mode of transport, so the accommodation boundary is a decision you make and document rather than one you look up.
- Does reusing a hotel towel reduce an event's carbon footprint?
- Reusing a towel reduces laundry, which is a genuine operational saving for the hotel, but it is not a reportable quantity for an event organiser. HCMI builds a room night's footprint from all energy used on site plus refrigerants, and includes outsourced operations such as laundry only where applicable.
- Where do you get a hotel emissions factor if the hotel will not give you one?
- From a published benchmark. The Cornell Hotel Sustainability Benchmarking Index draws on more than 31,500 member hotels across 94 countries and names business travel Scope 3 reporting as a use case for its data. National factor sets, such as the UK government's annual conversion factors, are the other route.
