Clients, sponsors and attendees sometimes ask an organiser what an event's carbon footprint was, and the answer is easier to give than it looks. Our hospitality industry page covers a venue's own annual footprint. This post is about the footprint of one event.
What to include
| Part | Data to collect | How it's counted |
|---|---|---|
| Travel to and from the event | Registration questions: starting point and mode | Passenger-km by mode (rail is 0.03092 kg CO2e per km in 2026) |
| Hotel nights | Room block bookings, by country | Room nights (a UK night is 10.4 kg CO2e) |
| Venue energy | The venue's metered kWh for your hire, or a share by area and hours | Electricity and gas factors |
| Catering | The caterer's invoice, or weights by food type if they can give them | Spend-based multiplier, or food factors |
| Waste | The venue's or contractor's weights by stream | Waste factors by material and treatment |
Print, merchandise, stand builds and AV equipment can be added as spend-based estimates if they are significant. Whatever you include, list it, and list what you left out.
A worked example
A one-day conference for 200 people in a UK city, with illustrative inputs and 2026 factors:
| Source | kg CO2e |
|---|---|
| Rail, 100 people, 200 km each way | 1,237 |
| Car, 70 people driving alone, 60 km each way | 1,394 |
| Domestic flights, 20 people, 450 km each way | 4,127 |
| Local bus, 10 people, 10 km each way | 20 |
| Hotel nights in the UK, 60 | 624 |
| Venue electricity, 3,000 kWh | 393 |
| Venue gas, 2,000 kWh | 365 |
| Catering, £9,000 (spend-based) | 2,336 |
| General waste, 0.4 tonnes to energy recovery | 2 |
| Food waste, 0.2 tonnes to anaerobic digestion | 2 |
| Total | 10,499 kg, or 10.50 tonnes |
That is about 52 kg per attendee. Travel is 65% of it. Each person who flew 450 km each way accounts for about 206 kg, against about 12 kg for each person who came 200 km each way by train. The flights use the government's figures including the extra warming effect at altitude.
Cutting an event's footprint
- Choose a venue near a main rail station, and say so in the joining instructions. Our post on train or plane has the numbers for common routes.
- Offer a strong online option for people who would otherwise fly in for one session. See video calls instead of travel.
- Plan catering to numbers and send leftovers and food waste to anaerobic digestion. In England, venues for temporary events, including outdoor ones, must already separate food waste and dry recyclables under the Simpler Recycling rules.
- Ask the venue for metered energy rather than an estimate, and for its renewable tariff, if it has one.
When you publish the figure, explain the method, show the per-attendee number and avoid calling the event "carbon neutral" unless you can back it up. Our guide to carbon offsetting explains what that claim needs.
How Carbon Recycling helps
Carbon Recycling is built for a company's annual footprint rather than one event, but it calculates every line above with the same DESNZ factors: flights entered by airport code with the distance worked out for you, rail, cars, hotel nights by country, venue energy, waste by material and treatment, and catering from spend. Your own staff's travel to the event, the venue hire and the catering go into your annual footprint with a description naming the event. Check venue energy figures quickly with the free kWh to CO2e calculator.