How High Do Planes Fly? Altitude & Flight Levels Explained

Look up at a jet leaving a contrail and it is natural to wonder just how high it is. This guide answers how high planes fly, explains cruising altitudes and flight levels, and shows how to read altitude on a flight tracker so you know what an aircraft is doing.

How high do commercial planes fly?

Most commercial jets cruise between 33,000 and 42,000 feet, with a typical figure around 35,000 to 38,000 feet. That is roughly 6 to 8 miles straight up.

The exact altitude depends on several factors:

• Aircraft type and weight. Heavier aircraft, or those early in a long flight with full fuel, often cruise lower and climb higher as they burn fuel off.
• Route and traffic. Air traffic control assigns altitudes to keep aircraft separated.
• Weather. Pilots may choose altitudes to avoid turbulence or find favourable winds.

Why do planes fly so high?

It comes down to thin air. At cruising altitude the air is far less dense than at the surface. That brings two big benefits:

1. Less drag. Thinner air means less resistance, so the aircraft uses less fuel to maintain speed.
2. Efficient engines. Jet engines are designed to run efficiently in these conditions.

Flying high also keeps aircraft above most weather, above terrain, and above slower or lower traffic. The result is a smoother, more economical flight.

What are flight levels?

Below a certain height (the transition altitude, which varies by country), altitude is given in feet above sea level. Above it, aircraft switch to flight levels based on a standard pressure setting.

A flight level is written as FL followed by the altitude in hundreds of feet:

So when a flight tracker shows FL350, the aircraft is at roughly 35,000 feet. Using a standard pressure setting ensures every aircraft measures altitude the same way, which keeps them safely separated.

Reading altitude on a tracker

Altitude is one of the most useful things a flight tracker shows, because it tells you what an aircraft is doing:

• Low and descending (a few thousand feet): on approach to a nearby airport.
• Low and climbing: just departed.
• High and steady (around FL350): cruising, likely passing over you on a longer journey.

Combine altitude with the callsign and route and you can read the story of the flight at a glance. Our guide on what plane is flying over your house puts this into practice.

See it for yourself

A flight tracker display makes altitude effortless to follow. PlaneTicker Desktop shows each aircraft's altitude alongside its callsign and route, colour-coded by flight phase, so you can tell at a glance whether the plane overhead is climbing away or settling into the cruise. Try it free in the browser demo.

Related reading

If altitude has caught your interest, you will probably enjoy how fast commercial planes fly, which explains cruising speeds and how they relate to altitude.