How high do planes fly? Cruising altitude explained

Most passenger jets cruise between about 31,000 and 42,000 feet, or roughly 9.5 to 12.8 km above the ground. That's about 6 to 8 miles up, higher than Mount Everest. Planes fly that high because the air is thinner, so they burn less fuel and stay above most of the weather.

Here's the simple explanation, plus what it means for you in your seat.

How high your plane flies depends on the aircraft, the length of the trip, and how heavy the plane is that day. Here's a rough guide to how high commercial planes fly, by type.

On a very short flight, the plane may never reach full cruising height. It finishes climbing and almost immediately starts its descent.

You'll also notice that pilots talk about height in feet, even in countries that use meters. When the captain mentions "flight level 350," that's simply shorthand for 35,000 feet.

It comes down to thinner air. At cruising altitude, the air is roughly a third as dense as it is at sea level. That brings several benefits:

• Less drag, less fuel. Thin air pushes back less, so the plane slips through it more easily and burns less fuel for every kilometer.

• Engines work best up there. Jet engines are designed to be most efficient in the cold, thin air at high altitude.

• Above most of the weather. Most clouds, rain, and storms sit lower down, so cruising is usually smoother.

• Room to spare. Height gives pilots time and space to handle any problem calmly, well clear of mountains, birds, and small aircraft.

• Helpful winds. Fast-flowing high-altitude winds, called jet streams, can give planes a tailwind that saves time and fuel.

There's a limit. Above about 42,000 feet, the air gets so thin that wings struggle to create enough lift and engines struggle to get enough air. The cabin would also have to hold back a much bigger pressure difference, which means a heavier, stronger body.

That's why most airliners are certified to fly no higher than about 41,000 to 43,000 feet. Lighter private jets can go a little higher.

Your cruising altitude is planned before you even board. The airline's flight plan picks the most efficient height for that day, based on:

• The plane's weight. A plane full of fuel often starts a little lower, then climbs in steps as it burns fuel and gets lighter.

• The winds. Pilots look for heights with a helpful tailwind, or at least a weaker headwind.

• The weather. Planned routes and heights steer around storms and bumpy air.

Air traffic control then fits every flight into its own slot in the sky. Planes are kept at least 1,000 feet apart vertically, and flights heading in different directions use different heights.

So if the captain announces a climb or a descent in the middle of the flight, it's usually routine. Pilots often change height to find smoother air or better winds.

You might be 10 km up, but the cabin doesn't feel like it. Planes are pressurized, so the air inside feels more like being in a mountain town.

Safety rules for airliners say the cabin must feel no higher than 8,000 feet (about 2,400 m) in normal flight. Newer planes like the Boeing 787 and Airbus A350 keep it closer to 6,000 feet (about 1,800 m), which many people find more comfortable on long flights.

A few things you may notice:

• Your ears pop. Cabin pressure changes as the plane climbs and descends. Swallowing, yawning, or chewing gum helps. Traveling with little ones? See our tips for flying with a baby or toddler.

• The air is dry. Humidity in the cabin is very low, so drink water regularly and go easy on alcohol and coffee.

• You may feel a little bloated. Gas in your body expands slightly at lower pressure. It's normal and passes after landing.

• It's freezing outside. The outside temperature at cruising height is often around -55°C. The cabin stays comfortable, but a light extra layer helps.

• Keep your seat belt on. Cruising is usually smooth, but turbulence can happen without warning. Keeping your belt loosely fastened while seated is the simplest way to stay safe.

How high can a plane fly?

Most airliners are certified to fly up to about 41,000 to 43,000 feet. Some private jets can reach 51,000 feet, and Concorde cruised at around 60,000 feet. Military and research aircraft have flown much higher.

Why do planes fly at 35,000 feet?

Around 35,000 feet is a sweet spot for most jets. The air is thin enough to cut drag and save fuel, but still dense enough for the wings and engines to work well. It also keeps the plane above most of the weather.

How high do planes fly in miles?

At a typical cruising altitude of 35,000 feet, a plane is about 6.6 miles (10.7 km) up. Most passenger jets cruise between roughly 6 and 8 miles high.

How high do private jets fly?

Private jets often cruise higher than airliners, usually around 41,000 to 45,000 feet, and some can reach 51,000 feet. Being lighter, they can climb above most airline traffic and weather.