IATA vs ICAO codes
Airports have two code systems. The IATA code is the 3-letter version you see on luggage tags and boarding passes — LHR, JFK, DXB. The ICAO code is 4 letters and used by pilots and air-traffic control — EGLL, KJFK, OMDB. The airport-code lookup accepts either.
How accurate is the flight CO₂ figure?
The calculator multiplies the great-circle distance by a per-passenger-kilometre emissions factor — 120 g/km for economy, 180 g for premium economy, 240 g for business, and 320 g for first. These match the order-of-magnitude figures used by major airline calculators (BA, Lufthansa) and offset providers. Actual numbers depend on aircraft type, load factor and route, so treat this as a useful comparison number rather than a precise emissions statement.
Carry-on rules vary much more than you think
Cabin-bag sizes range from 40×20×25 cm (Ryanair free bag) to 61×41×28 cm (Southwest). Most major airlines centre around 55×40×23 cm, and most enforce a weight limit too — anywhere from 7 kg (Emirates, Singapore) to 23 kg (British Airways). If you fly multiple airlines, pick a bag that fits the smallest carry-on you'll face on the trip.
Is upgrading worth it?
For a long-haul flight, the jumps that change the most are pitch (legroom) and whether the seat lies flat. Economy is typically 31–32" pitch. Premium economy adds 5–8" and better recline. Business is usually lie-flat above 75". First adds a suite. Compare across airlines on the Class tab to see whether your specific aircraft justifies the fare difference.