Why Do Jets Fly Higher Than Mount Everest?

Airliners like the Boeing 777 cruise around 35,000 feet, higher than Mount Everest. Up there the air is only about a third as dense as at sea level. Less air to push through means less drag, so the jet flies faster on less fuel. Go too high, though, and the wings and engines don't get enough air. Cruise altitude is the sweet spot.

Notes: -65°F is the standard-atmosphere value at 35,000 ft; real temperatures vary. Actual cruise levels depend on aircraft, weight and route (typically ~31,000–42,000 ft). Mountain shape is stylized; its height is to scale.

Sources:
– ICAO Standard Atmosphere (UK CAA, Principles of Flight):
– FAA time of useful consciousness (AC 61-107B), summarized:
– Mount Everest height, 2020 survey:
– NASA Glenn, drag equation:
– Boeing 777 cruise altitude: