FTCfly gives quick, clear estimates. This page explains exactly how those numbers are produced and where their limits are, so you can use them sensibly.
How we estimate flight time
For two airports we work out the great-circle distance (the shortest path over the curved Earth) from their coordinates using the haversine formula, divide it by an average cruise speed of about 800 km/h, and add roughly 30 minutes for taxiing, take-off, climb, descent and landing. Arrival time is then converted into the destination's local time using the IANA time-zone database.
Why the real flight can differ
Our figure is an estimate for a single nonstop leg. Real flights vary because of:
- Winds and the jet stream. Eastbound flights ride a tailwind and are faster, while westbound is slower.
- Routing. Real air-traffic routes are a few percent longer than the straight line.
- Aircraft type and its cruising speed.
- Connections. Layovers and the detour via a hub add a lot of time.
In practice, estimates are usually within about 15% of the published schedule, but this is not guaranteed.
Not for operational use
FTCfly is for general information and trip planning only. Please do not use it for booking decisions, catching connections, flight operations, navigation, or anything safety-critical. Always confirm with the airline or operator. The CO₂ and jet-lag figures are general guideline estimates too.
Data sources
Airport coordinates and time zones come from OpenFlights (ODbL), and the world map outline is from Natural Earth (public domain). OpenFlights is no longer actively maintained, so a few airports opened in recent years are missing from it. Where that affects a major hub I add the airport myself from a sourced record rather than leaving a gap — Istanbul Airport (IST), added 23 August 2026 from OurAirports, is the current example. Data can still contain errors or be out of date, so please report anything wrong and I will fix it.
How the CO₂e figure is worked out
The carbon figure is CO₂-equivalent per passenger, economy class, using the UK DESNZ 2026 greenhouse-gas conversion factors ("Business travel – air"), including radiative forcing — that is what makes it CO₂e rather than CO₂ alone, because aviation's warming effect is not only the carbon. Two figures are used: 0.12576 kg CO₂e per passenger-kilometre for flights under about 3,700 km, and 0.11704 above that.
One detail that matters for a great-circle calculator: those DESNZ factors already build in an 8% distance uplift to account for aircraft not flying the most direct route — airspace avoidance, stacking, air-traffic routing. That is precisely the difference between the straight-line distance this site computes and the track an aircraft really flies, which is why applying them to a great-circle distance is reasonable rather than an under-count. These are the UK-reported factors, used here as a global proxy, and they assume a typical load factor and seating mix — so treat the result as an order-of-magnitude guide, not an audit-grade number for your specific flight.
Correction, 23 August 2026: earlier versions of this site labelled the carbon figure "DEFRA 2023" and used factors of 0.156, 0.097 and 0.081. Those values do not match any published DEFRA figure, with or without radiative forcing, so both the numbers and the citation were wrong. They have been replaced with the sourced DESNZ 2026 factors above.
Advertising and affiliate disclosure
FTCfly may display third-party advertising and may contain affiliate links, for example to eSIMs, travel insurance, airport transfers or booking sites. If you buy through an affiliate link, we may earn a small commission at no extra cost to you. This never influences the flight-time numbers, which are pure calculation, and we only suggest things we think are genuinely useful to travellers.
Contact
Questions? Email hello@ftcfly.com.