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Personal flight carbon calculator

Count your holiday flights honestly: passenger-km times DEFRA 2025 factors, radiative forcing included — one long-haul return can outweigh a year of home electricity.

Prefer to skip the typing? Upload the bill instead — the numbers get read for you, three documents a day free.

How this calculation works

This is the same method — and the exact same emission factors — that we apply to business travel. Holiday flights don't get a softer arithmetic:

Emissions (kgCO₂e) = passenger-kilometres flown × flight emission factor (kgCO₂e per passenger-km)

A passenger-kilometre is one person carried one kilometre. One traveller flying 5,000 km is 5,000 pax-km; a family of four on the same route is 20,000. Count every leg, and remember that a return trip doubles the distance — that's why the long-haul placeholder above reads 21,760 pax-km for a single traveller flying Singapore–London and back.

The factor differs by flight length for a physical reason: takeoff and climb burn a disproportionate share of fuel, and on a short flight that overhead is spread over fewer kilometres. This is why the short-haul domestic factor (0.25397 kgCO₂e per pax-km) is higher per kilometre than the long-haul one (0.19085) — even though a long-haul flight emits far more in total, it cruises efficiently for most of its distance.

One more honesty setting: the factors we use include the radiative forcing uplift — an adjustment for the additional warming caused by non-CO₂ effects at altitude, such as contrails and nitrogen oxides. The science on the exact size of that uplift is still evolving, but excluding it entirely understates what flying does to the climate, so we count it by default.

The factors

This calculator uses the UK DEFRA/DESNZ 2025 greenhouse gas conversion factors for passenger air travel — average passenger, with radiative forcing — published under the Open Government Licence v3.0:

| Flight type | Factor (kgCO₂e per pax-km) | From Singapore, that means | | --- | --- | --- | | Short-haul domestic | 0.25397 | Domestic legs inside another country (Singapore has none) | | Short-haul international | 0.15353 | Under ~3,700 km — Bali, Bangkok, Kuala Lumpur | | Long-haul international | 0.19085 | Over ~3,700 km — London, Sydney, Tokyo |

A note on cabin class. These are average-passenger factors. If you fly premium economy, business, or first, your seat occupies more of the aircraft's floor space, so your real share of its emissions is higher than the average passenger's; an economy seat sits slightly below it. This free calculator does not apply a cabin-class adjustment — if you turned left when boarding, read your result as a lower bound.

As with every calculation on this site, the factor, source, year, and licence are printed under your result, so the provenance travels with the number.

A worked example

Take the trip most Singapore households recognise: one traveller, Singapore to London return, roughly 21,760 passenger-km for the round trip.

21,760 pax-km × 0.19085 kgCO₂e/pax-km = 4,152.9 kgCO₂e ≈ 4.15 tCO₂e

A family of four on the same itinerary is 87,040 pax-km — about 16.6 tCO₂e for one holiday.

Now the comparison that makes flights worth counting honestly. Divide that single traveller's 4,152.9 kgCO₂e by Singapore's current grid emission factor of 0.4020 kgCO₂e/kWh (EMA, 2024 data year) and you get roughly 10,331 kWh of grid electricity — call it ten thousand kilowatt-hours. Most flats and condos draw well under that in a year, which means one long-haul return trip can exceed your home's entire annual electricity footprint. If you only track one personal number beyond your utility bill, make it this one.

For scale in the other direction: a regional holiday totalling 3,000 passenger-km round trip (short-haul international) works out to 3,000 × 0.15353 = 460.6 kgCO₂e ≈ 0.46 tCO₂e — about a ninth of the London trip. Distance, not frequency, is what dominates a flight footprint.

What an uploaded boarding pass actually calculates

The form above uses one flat, average-passenger factor per pax-km, which is the right level of detail for a quick personal estimate. If you instead upload the e-ticket, the extraction pipeline does something more granular: it resolves the real departure and arrival airports, computes the great-circle distance itself, adds an 8% path-uplift for realistic routing, and applies a cabin-class multiplier — 1.0 for economy, 1.6 for premium economy, 2.9 for business, 4.0 for first — alongside the radiative forcing adjustment.

Take a honeymoon trip, one traveller, Singapore–London return, booked in business class:

Great-circle distance: 10,880 km × 1.08 path-uplift = 11,750.4 km actual 11,750.4 km × 0.19085 kgCO₂e/pax-km (long-haul factor) = 2,243.1 kgCO₂e 2,243.1 × 2.9 (business-class multiplier) = 6,505.0 kgCO₂e 6,505.0 × 1.9 (radiative forcing index) = 12,359.6 kgCO₂e outbound Return leg (same route): another 12,359.6 kgCO₂e → 24,719.2 kgCO₂e ≈ 24.72 tCO₂e

One transparency note on that stack: the base factor is DEFRA's average-passenger series, which already reflects radiative forcing, and the pipeline then applies its own explicit 1.9x index on top. That is a deliberately cautious stacking, and it is why uploaded flight numbers run higher than the manual form for the identical journey — every multiplier applied is listed in the methodology line under the result, so nothing is hidden in the arithmetic. If you want the strictly DEFRA-basis estimate, the manual form above gives you exactly that.

Compare that with the economy-class worked example earlier on this page for the identical route: 4,152.9 kgCO₂e. Same traveller, same airports, same return trip — but the business-class result is nearly six times larger, driven almost entirely by the cabin multiplier and radiative forcing index stacking together. If you flew up front, the flat-factor number above is a meaningful underestimate of your actual seat's footprint.

Common mistakes we see

  • Entering one-way distance for a round trip. It's an easy slip — the London example above needs both legs summed (21,760 pax-km), not just the 10,880 km one-way distance.
  • Treating connecting flights as a single leg. A Singapore–Tokyo–Los Angeles itinerary is two legs with two different great-circle distances, not one long-haul segment measured end to end.
  • Skipping cabin class for premium travel. As shown above, a business-class long-haul return can run close to six times the economy-blend figure this calculator produces by default.
  • Confusing flight count with flight distance. Four short regional hops can still add up to less than one long-haul return — distance, not the number of boarding passes, is what drives the total.

What this calculator doesn't cover

Honesty about limitations is part of the method:

  • Cabin class. As above — the factor is the average passenger. Premium cabins carry a higher real share per person; we don't model it.
  • Route precision. Your pax-km figure is an estimate. Actual flight paths run longer than straight-line distance, aircraft types differ, and per-flight tools that know your exact plane will produce different numbers. This calculator is built for honest, order-of-magnitude personal accounting with a published, licensed factor — not per-tail-number precision.
  • Offsets and sustainable aviation fuel. If you paid for carbon offsetting at checkout or your airline claims SAF use, none of that is netted off here. The result is your gross emissions; what you do about them is a separate decision.
  • The rest of the trip. Taxis to Changi, hotel room-nights, and meals are real but separate lines — hotel stays in particular have their own published factors and aren't folded into your flight number.
  • Radiative forcing uncertainty. The uplift is included because leaving it out understates the impact, but the multiplier itself is an active area of atmospheric science. Treat flight numbers as honest estimates, not measurements.

Where this fits in your reporting

It may seem odd that a holiday-flight tool cites the same sources an organization's disclosure would. That's deliberate. Business air travel falls under Scope 3, category 6, for any company, nonprofit, school, or agency that sends people places — and the method any of them will use for flights is exactly what you see here: passenger-km multiplied by a published DEFRA-style factor. If you work somewhere that supplies listed customers or reports under a framework like ISSB IFRS S2 or GRI 305, the travel question is coming to your inbox in a questionnaire; having done the same arithmetic on your own holidays means nothing about it will be unfamiliar. The office side of that story starts with the business electricity calculator, and Singapore-listed readers can check exact filing dates in our SGX climate reporting deadlines guide.

And when you'd rather not measure route distances by hand, upload your e-ticket or itinerary — the same factors get applied to details read straight off the document, with a confidence score on every extracted field. No signup is needed: three document uploads a day anonymously, ten a day with an email address, and files are deleted automatically after 30 days.

Sources

Frequently asked questions

Why do you count passenger-kilometres instead of number of flights?
Because a Singapore to Bangkok hop and a Singapore to London return are wildly different flights. Passenger-km is travellers multiplied by route distance: one person flying 5,000 km is 5,000 pax-km, and a family of four on the same route is 20,000. It is also the unit the DEFRA conversion factors are published in, so no translation is needed.
Do these factors include non-CO2 effects like contrails?
Yes. We use the DEFRA/DESNZ 2025 flight factors with the radiative forcing uplift, which accounts for the extra warming from non-CO2 effects at cruising altitude. Excluding it makes flying look materially smaller than its real climate impact, so we include it by default.
Does flying business class or premium economy change my number?
It should, but this calculator does not adjust for it. The factors represent the average passenger on the aircraft. A premium seat takes up more floor space, so your true share of the plane's emissions is higher than average — treat the result as a floor, not a ceiling, if you fly up front.
Where is the line between short-haul and long-haul?
Around 3,700 km per flight, following the DEFRA distance banding. From Singapore, Bali, Bangkok and Kuala Lumpur are short-haul international; London, Sydney and Tokyo are long-haul. The short-haul domestic field is for domestic legs inside another country — Singapore itself has no domestic flights.
Should I count flights my employer paid for?
For a personal footprint, count the trips you chose to take. Flights taken for work belong in your employer's Scope 3 business-travel line — same method, same factors, different ledger. If you counted them in both places, the emissions would be double-reported.
I booked a multi-city trip — how do I add that up?
Sum each leg on its own route distance rather than using the origin-to-final-destination distance. Singapore to Bangkok to Tokyo to Singapore is three legs, each with its own great-circle distance and haul band, not one figure covering the whole loop.
Does it matter which airline I flew, or whether it was a budget carrier?
Not for this method. The DEFRA factors are averaged across an entire haul band regardless of airline, so a budget short-haul carrier and a full-service one get the same factor. What changes the number is distance and cabin class, not the airline's brand.
If I upload my boarding pass instead of typing the distance in, will I get the same result?
Not quite. Uploaded tickets go through a more detailed pipeline that resolves the actual airports, computes the great-circle distance, adds an 8% path-uplift, and applies a cabin-class multiplier on top — see the worked example below for how much that can move the number, especially if you flew business or first.