The short answer
In the United States a drone may not fly above 400 feet (121.92 m) above ground level. In the European Union and the UK the equivalent cap is 120 m (393.7 ft). The two limits are within 6 feet of each other and were set for the same reason: to keep small unmanned aircraft below the altitude floor where manned aircraft operate.
Both limits are measured above the ground directly below the drone, not above sea level. A drone flying over a hillside that rises 200 ft climbs 200 ft with it and stays legal. The same drone hovering at a fixed barometric altitude while the ground falls away below it does not.
The FAA rule and where the number comes from
Section 107.51 of the Federal Aviation Regulations sets the ceiling for commercial drone operations at 400 ft AGL. Recreational flyers are held to the same figure by 49 USC 44809. There is no meaningful altitude difference between the two categories in the US.
The number is derived from the rule that governs manned aircraft. Under 14 CFR 91.119, an aircraft may not be operated below:
| Situation | Manned aircraft minimum |
|---|---|
| Over congested areas (cities, towns, open-air assemblies) | 1,000 ft above the highest obstacle within a 2,000 ft radius |
| Over other than congested areas | 500 ft above the surface |
| Over open water or sparsely populated areas | 500 ft from any person, vessel, vehicle, or structure |
| Takeoff and landing | No minimum |
The binding constraint is the 500 ft figure. Setting the drone ceiling at 400 ft leaves a 100 ft (30.48 m) vertical buffer between the top of legal drone airspace and the bottom of legal manned airspace. That buffer absorbs altimeter error, GPS drift, and the fact that a pilot judging 500 ft by eye is not precise.
The buffer is thin, and it is the reason the exceptions in 91.119 matter so much to drone operators. Helicopters are exempt from the 500 ft floor if the operation is conducted without hazard, and agricultural aircraft, medevac helicopters, and law enforcement routinely operate below 500 ft. Those are the aircraft a drone actually risks meeting, not airliners at 12,000 m.
The structure exception
The most useful and most misunderstood part of the US rule is the structure exception in 107.51(b):
A drone may exceed 400 ft AGL if it remains within 400 ft of a structure and does not fly more than 400 ft above that structure’s uppermost limit.
Both conditions apply at once. The horizontal 400 ft is a radius from the structure, and the vertical 400 ft is measured from the top of the structure, not from the ground.
| Structure | Structure height | Legal drone ceiling within 400 ft radius |
|---|---|---|
| Two-story house | 20 ft (6.1 m) | 420 ft (128 m) |
| Cell tower | 300 ft (91.4 m) | 700 ft (213 m) |
| Wind turbine (modern onshore) | 500 ft (152 m) | 900 ft (274 m) |
| Skyscraper | 1,000 ft (305 m) | 1,400 ft (427 m) |
| Broadcast mast | 1,500 ft (457 m) | 1,900 ft (579 m) |
This is what makes commercial inspection work possible. Surveying the blades of a turbine whose tip reaches 152 m requires flying well above 121.92 m, and the exception permits it as long as the aircraft stays tucked against the structure. Step 500 ft laterally away from the tower at 700 ft and the flight becomes illegal instantly.
The exception does not stack with airspace authorization. In controlled airspace the LAANC ceiling still applies, and it is often lower than 400 ft. Grid cells around an airport are published at 0, 50, 100, 200, 300, or 400 ft, and a cell marked 100 ft caps the flight at 100 ft regardless of what structure stands there.
Europe: the 120 m Open category
EASA regulation 2019/947 splits drone operations into three categories. The Open category, which covers essentially all consumer and light commercial flying, is capped at 120 m above the closest point of the earth’s surface.
| Subcategory | Drone class | Where you can fly | Height cap |
|---|---|---|---|
| A1 | C0 (under 250 g), C1 (under 900 g) | Over people, not over assemblies | 120 m |
| A2 | C2 (under 4 kg) | 30 m from uninvolved people, 5 m in low-speed mode | 120 m |
| A3 | C3, C4 (under 25 kg) | 150 m from residential, commercial, industrial areas | 120 m |
Europe has its own obstacle exception, worded differently from the US one: when flying within 50 m horizontally of an obstacle taller than 105 m, the height limit becomes 15 m above the obstacle’s height. That is a much tighter allowance than the American 400 ft radius and 400 ft vertical, and it reflects a more conservative approach to how far above an obstruction an aircraft should be permitted to climb.
Anything beyond the Open category limits falls into the Specific category, which requires an operational authorization from the national aviation authority, backed by a SORA risk assessment. That is the route used for beyond-visual-line-of-sight delivery, long linear infrastructure survey, and higher-altitude work.
The UK left the EU regulatory system but kept the same numbers. The CAA Drone and Model Aircraft Code specifies 120 m and describes it in the guidance as 400 ft, which is a rounding of 393.7 ft.
AGL versus MSL, and the altimeter problem
Nearly every drone incident report involving altitude comes down to one confusion: above ground level versus above mean sea level.
Drone flight controllers report height relative to their takeoff point. Launch from a ridge at 500 m elevation, fly out over the valley, and the app may read 100 m while the aircraft is 400 m above the valley floor. The app is telling the truth about its own reference and lying about the one that matters legally.
Aviation charts use MSL for almost everything above the surface, which is the opposite convention. Flight levels, the pressure altitudes used in the cruise, are a third system again, referenced to a standard 1013.25 hPa datum rather than to local pressure. Our guide to flight levels covers why airliners switch reference systems at the transition altitude and why FL350 is not 35,000 ft above the ground.
Two practical consequences for drone pilots:
- Fly the terrain, not the number. If the ground rises ahead of you, descend to keep the actual clearance under 400 ft. Some flight apps offer terrain-follow modes that do this automatically from elevation data.
- Treat the barometric reading as approximate. Consumer barometric altimeters drift by 3 to 5 m over a flight as local pressure and temperature change. Plan to fly at 350 ft rather than 399 ft.
Physical ceilings versus legal ones
The legal limit is far below what the hardware can do, but not as far as most people assume.
| Altitude | What happens |
|---|---|
| 124 m (about 400 ft) | Legal ceiling in most of the world |
| 500 m (1,640 ft) | Default firmware cap on most consumer drones |
| 3,000 m (9,843 ft) | Manufacturer-rated service ceiling for many prosumer models |
| 5,000 m (16,404 ft) | Thrust margin becomes marginal, hover requires most of available power |
| 6,000 m (6,119 m is a common Himalayan reference) | Only lightly loaded, high-altitude-optimized aircraft remain controllable |
The limiting factor is air density, not power. A propeller produces thrust proportional to the density of the air it moves, and density falls to about half of sea level value by 5,500 m. A multirotor that hovers at 50 percent throttle at sea level is hovering near full throttle there, leaving nothing for maneuvering, wind, or descent recovery. Battery performance degrades in the cold at the same time, and both effects compound.
None of that changes the rule. The ceiling is a separation standard, not a performance standard, and it exists so that the airspace between the ground and 500 ft stays predictable for the aircraft that have to use it. For converting any of the values in this guide, the free meters-to-feet calculator covers arbitrary altitudes, and why aircraft cruise at 36,000 feet explains what happens in the airspace far above the drone layer.
Sources and further reading: