Depending on the route and flying conditions, most commercial aircraft cruise anywhere between 33,000 ft and 39,000 ft. At high altitudes, the air density is much less, allowing for less turbulence and aerodynamic drag in the thin air. The designed service ceiling of many commercial airliners is 43,000 ft. An aircraft's service ceiling is designed based on the aircraft weight, engine power, and the amount of lift the wings can generate.