Cruising altitude is the steady height an aircraft maintains during the long middle portion of a flight, after climbing away from the departure airport and before descending toward the destination. For most commercial jets this sits between 9,000 and 12,000 metres (roughly 30,000–40,000 ft).
Why do planes fly so high?
The air near the ground is thick. Up at cruising altitude it’s much thinner — often less than a third of the density at sea level. That thin air is exactly what airliners want:
- Less drag — thinner air pushes back less against the aircraft, so the jet burns far less fuel to hold its speed.
- Efficient engines — jet engines are designed to run most economically in cold, thin, high-altitude air.
- Above the weather — most storms, turbulence, and clouds sit lower down. Cruising high means a smoother, more predictable ride.
- Room to glide — altitude is a safety buffer. If something goes wrong, height buys the crew time and distance.
Flight levels: how altitude is described
Above a certain height, pilots and controllers stop using feet directly and switch to flight levels (FL). A flight level is the altitude in hundreds of feet, based on a standard air-pressure setting.
- FL350 means 35,000 ft
- FL400 means 40,000 ft
Using one shared pressure reference keeps every aircraft’s altitude readings consistent, so planes stay safely separated even when local air pressure varies.
What you’ll see on the radar
On the FlyOverhead radar, the altitude shown for a jet at cruise is usually somewhere around FL350–FL400. A plane that’s much lower is probably still climbing out or descending toward an airport near you.
Different aircraft favour slightly different cruising altitudes depending on their weight and engines — a light narrowbody may sit a little higher than a fully loaded widebody on the same route.