Why do planes fly at 35,000 feet?
Thin air means less drag and better fuel economy, and cruising that high keeps jets above much of the weather. Go too high, though, and wings and engines run short of air.
Quick Answer
Airliners typically cruise around 35,000 feet because it’s a sweet spot. The air there is far thinner than at sea level, so the plane pushes through less of it and the engines burn less fuel per mile. The air is also frigid, about −54°C (−65°F) in a standard atmosphere, which helps jet engines run efficiently. Cruising that high also puts planes above much of the weather, since nearly all weather happens in the lowest layer of the atmosphere, the troposphere. The catch is that wings need air to make lift and engines need oxygen to burn fuel, so every airliner has a ceiling. Inside, you’re comfortable because the cabin is pressurized to the equivalent of 8,000 feet or lower.
By the Numbers
Key Facts
- Why so high
- Thinner air means less drag and lower fuel burn per mile
- Outside temperature
- About −54°C (−65°F) in a standard atmosphere
- Cabin pressure
- Kept at the equivalent of 8,000 feet or lower, by FAA rule
- The weather
- Almost all of it happens in the troposphere, 4 to 12 miles up depending on latitude
Sea level vs. 35,000 feet
| Sea level | 35,000 feet | |
|---|---|---|
| Air pressure | 100% | About 24% |
| Standard temperature | 15°C (59°F) | About −54°C (−65°F) |
| Clouds and storms | All around | Much of it below |
Thin air, less drag
The higher a plane climbs, the thinner the air, so it pushes through less of it. That means less drag, and the engines don’t have to work as hard to hold cruising speed, which saves fuel on every mile.
Above much of the weather
Nearly all weather happens in the troposphere, the lowest layer of the atmosphere, which reaches about 4 miles high near the poles and 11 to 12 miles near the equator. Cruising near 35,000 feet keeps jets above many clouds and storms, though the tallest thunderstorms can tower even higher.
Why not go even higher?
Wings need air to generate lift and engines need oxygen to burn fuel. Every airliner has a ceiling where the thin air leaves too little margin, so crews fly at the most efficient altitude for the plane’s weight, often climbing in steps as fuel burns off and the plane gets lighter.
Myth vs. Fact
MythHigher is always better.
FactAbove a plane’s best altitude, the air gets too thin for its wings and engines to work efficiently.
MythPlanes fly high just to avoid turbulence.
FactFuel efficiency is the big reason. Clearing much of the weather is a bonus, and turbulence can still happen at cruising altitude.
The Bottom Line
Planes cruise around 35,000 feet because thin air cuts drag and fuel burn, and that altitude clears much of the weather. Climb much higher and wings and engines start running short of air.
