Flight Carbon Footprint Calculator (CO₂e per trip)

Understanding the flight carbon footprint calculator — concept and principle

This calculator estimates the greenhouse-gas emissions of a flight per passenger, using the UK government's (DESNZ) 2025 conversion factors. Pick two airports or enter a distance, choose the cabin class and trip type, and it returns kilograms of CO₂ equivalent. Travellers, companies reporting business travel and students use it to compare trips.

How it is calculated

1. Great-circle distance between the airports on a sphere of radius 6,371 km (haversine formula).
2. Distance counted = great-circle distance × 1.08 (8% uplift for indirect routes and holding) × 2 for a return trip.
3. Factor (kg CO₂e per passenger-km, with radiative forcing): domestic 0.229; short-haul up to 3,700 km economy 0.126, business 0.189; long-haul economy 0.117, premium economy 0.187, business 0.339, first 0.468.
4. Without radiative forcing, the factor is divided by 1.7.
5. Footprint = distance counted × factor × passengers.

The principle

A plane's fuel burn, and so its CO₂, grows with distance, and is shared among the seats on board. Larger seats in business and first class take more cabin space, so each carries a bigger share of the flight's emissions. Short flights have higher emissions per km because take-off and climb use a lot of fuel. Aircraft also affect the climate through contrails and nitrogen oxides at altitude; DESNZ recommends including these non-CO₂ effects with a multiplier (radiative forcing), which is why the default factors are 1.7 times the CO₂-only values.

Worked example

Default inputs: Seoul Incheon (ICN) to Los Angeles (LAX), one way, economy, 1 passenger, international, radiative forcing included.

1. Great-circle distance = 9,627 km, which is over 3,700 km: long-haul.
2. Distance counted = 9,627 × 1.08 = 10,397 km.
3. Factor = 0.117 kg CO₂e per passenger-km.
4. Footprint = 10,397 × 0.117 = 1,216 kg CO₂e = 1.22 tonnes per passenger.

How to read the result

The biggest levers are flying less, choosing economy, and taking direct flights. Compare options by changing the cabin or route. Numbers from airlines or other calculators may differ because they use different load factors, aircraft data or treatment of non-CO₂ effects.

Common mistakes

• Forgetting to select return for a round trip.
• Comparing a figure with radiative forcing to one without.
• Counting a connecting itinerary as one great-circle distance; add each leg.
• Assuming offsets cancel the emissions released.

Frequently asked questions

How much CO₂ does a flight from Seoul to Los Angeles emit?

About 1.2 tonnes CO₂e per economy passenger one way with DESNZ 2025 factors including non-CO₂ effects.

Why does business class have a higher footprint?

Bigger seats take more space, so each seat carries a larger share of the flight's emissions.

What is radiative forcing in flight calculators?

An allowance for warming effects beyond CO₂, such as contrails and nitrogen oxides at altitude.

Sources: UK Department for Energy Security and Net Zero, "Greenhouse gas reporting: conversion factors 2025", Business travel – air