What does a flight emit? Calculate CO₂ and understand the result

What determines a flight’s footprint?

There is no single figure for every flight. Distance, aircraft, occupancy and cabin class can affect the result. Include every leg of a connecting flight and the return journey.

Calculators may differ because they use different route adjustments, emission factors and boundaries. Compare methods as well as totals.

What is the difference between CO₂ and CO₂e?

CO₂ is a particular greenhouse gas. CO₂e is a shared unit for comparing greenhouse gases. Aviation also affects climate through other processes, including contrails, so a CO₂-only figure does not necessarily cover the full climate effect.

The UK government’s factors illustrate how flight category, cabin class and uplifts affect calculations. This source explains method choices; the figures below describe Treesy’s current defaults, not official 2026 conversion factors.

Source: UK Government: 2026 greenhouse gas conversion factors — methodology

How does Treesy’s travel calculator work?

For each flight leg, the tool calculates the distance between the selected airports, adds a fixed 10% route adjustment and multiplies by a standard factor per passenger kilometre.

Default factors are 0.255 kg CO₂e per km for distances below 500 km, 0.156 for 500–3,700 km and 0.150 for longer distances. Category selection uses the distance before the adjustment. The calculator does not distinguish individual aircraft, occupancy or cabin class.

This is an estimate with fixed assumptions. The source year for the default factors and their treatment of non-CO₂ climate effects are not yet documented in the tool’s method basis. We do not describe the output as complete or verified. Formal business reporting needs a documented, current factor set and retained calculation evidence.

Worked example: 1,000 km each way

For a hypothetical journey of 1,000 km between airports each way and one passenger, Treesy’s default model gives: 1,000 × 1.1 × 0.156 = 171.6 kg CO₂e outbound. The return trip totals 343.2 kg CO₂e.

Four passengers on that return journey total 1,372.8 kg, or 1.3728 tonnes CO₂e. At 10 trees per tonne, the contribution model suggests 13.728 trees, rounded up to 14. This determines a contribution and does not establish that the trip has been offset.

Hotel stays and airport transfers are excluded from this example. Add them separately when estimating the whole trip.

What should I enter?

Work through the complete itinerary:

• Enter each flight leg, including connections and the return trip.
• Check whether the result covers one person or the group before multiplying.
• Include train, bus, car or ferry legs where relevant.
• Add accommodation and check the unit used for nights.
• Retain itinerary, calculation date, factors and boundaries when using the estimate in a quote.

How can I reduce my travel footprint?

Start with the number of trips and transport choice. Consider remote meetings, combining visits or taking a train where practical. Compare options with matching boundaries.

A travel agency can explain what an estimate covers and offer planting as a separate contribution. Customers can fund planting alongside efforts to reduce travel emissions. The contribution does not change the flight’s own emissions.

Can I use this for business emissions reporting?

The tool provides an initial estimate and helps identify activities to include. It does not replace a reviewed calculation for a specific reporting standard. A report needs to identify activities, factors, reference years and climate effects covered.

If your travel provider or adviser already has a documented calculation, Treesy can use it as the basis for the tree count. Keep that travel calculation and the planting contribution separate.