For most office-based organisations, flights are the largest single item in scope 3 and often larger than scope 1 and 2 combined. They are also one of the few scope 3 items where exact data exists for every single event. This guide is about using it.
Where flights sit in the frameworks
- GHG Protocol. Employee flights are scope 3, category 6 (business travel). Flights by consultants or visitors that you pay for usually belong in the same category; commuting is category 7.
- CSRD / ESRS E1. Companies reporting under the EU Corporate Sustainability Reporting Directive disclose scope 3 in tonnes of CO₂e under ESRS E1-6, by category where significant. The scope of CSRD has been revised since 2024, so check with your auditor which reporting wave applies to you.
- Science-based targets. If scope 3 is more than 40 % of your total, a target under SBTi has to cover it. Business travel is usually part of that.
Three ways to calculate, in increasing accuracy
Spend-based. Travel cost × an emission factor per currency unit. Quick, and about as precise as it sounds: a cheap seat on a full low-cost flight gets a lower number than an expensive seat on the same aircraft, even though the fuel is the same.
Distance-based. Great-circle distance between airports × a factor per passenger-kilometre, usually by distance band and cabin class. This is what most calculators and conversion-factor tables do. It is reproducible and cheap, and it cannot see which airline, which aircraft or how full the flight was. Two organisations with identical travel patterns get identical numbers, no matter what they changed.
Flight-based. Each flight is identified by flight number and date and calculated with the aircraft that flew it, the operator’s cabin layout and occupancy, and the distance actually flown. This is what Carbon Compute does. The number moves when your travel policy moves: choosing a direct flight, an economy seat or an airline with fuller aircraft shows up in the result.
The GHG Protocol’s scope 3 guidance allows all three. It asks you to pick the most accurate method your data supports and to be consistent.
What an auditor will ask for
Limited assurance of sustainability reports is now the norm in the EU. For flights, expect questions like these:
- Where did the trip data come from? Travel-agency or booking-tool exports are the usual answer. Expense reports fill the gaps.
- How was each flight calculated? A method description, the emission factors and their version, and the height factor if any.
- Can you reproduce this number? Flight-level data makes this a lookup instead of an argument.
- Did anything change since last year? Method changes should be stated and, ideally, earlier years restated.
The data to keep
For every flight segment:
| Field | Why |
|---|---|
| Flight number and date | Identifies the aircraft, route and operator |
| Origin and destination | Distance and routing |
| Cabin class | Seat size weighting |
| Number of passengers | Multiplier |
| Cost centre or department | Lets you act on the result |
Most travel-agency exports already contain all of this. If yours does not include flight numbers, a route and date is often enough to identify the flight.
From report to reduction
A report tells you the total. Flight-level data tells you why: which ten routes, which departments, which share is long-haul business class. That is where a reduction target becomes a travel policy. Carbon Wiz is built around exactly that step: the same per-flight calculation, visualised by route, department and trend, with action cards you can drag onto next year’s budget to see what they would do.
If you would like to see how your own data would look, contact us for a demo.