How high do drones fly?

A drone's altitude depends on the type of aircraft and who's flying it. Civilian drones used by hobbyists and businesses are legally limited to 120 m (400 ft) above the ground in the European Union, under EASA regulations, and to the same 400 ft in the United States under FAA rules. The reason is to keep them separated from crewed aviation, which, except during takeoff and landing, rarely flies below 150 m (500 ft). Exceeding that ceiling requires specific authorization from the aviation authority.

Military drones fly at altitudes comparable to crewed aircraft. The MQ-9 Reaper, the most widely used among Western air forces, has a service ceiling of 15,240 m (50,000 ft) according to the USAF, although on missions it usually patrols between 6,000 and 9,000 m, high enough to go unheard from the ground and stay out of range of light weapons. The RQ-4 Global Hawk strategic surveillance drone climbs to 18,288 m (60,000 ft) and stays there for more than 30 hours. At the opposite extreme, small quadcopters and the single-use attack drones used in Ukraine operate at altitudes of just tens of meters, sometimes skimming treetops, to avoid radar detection.

There's a third category, the so-called high-altitude pseudo-satellites (HAPS), such as the Zephyr developed by Airbus: very light solar-powered aircraft that climb above 20,000 m, where there are no clouds or traffic, and remain airborne for weeks as communications or observation platforms. Their limit is no longer the law or the engine, but the structural fragility against tropospheric turbulence during climb and descent.