What is AGL (Above Ground Level)?
AGL means Above Ground Level — altitude measured from the surface of the earth directly below the aircraft, not from sea level. Part 107 limits drones to 400 ft AGL for most operations.
AGL contrasts with MSL (Mean Sea Level), which measures altitude from sea level. For drones, AGL is the relevant unit because it tracks how high you are above the ground you're operating over — which determines obstacle clearance, line-of-sight, and your relationship with crewed aircraft (which fly MSL altitudes above 1,000 ft, but use AGL for traffic patterns and approaches).
Part 107 § 107.51 limits drones to 400 ft AGL except when within 400 ft of a structure, in which case the drone may operate up to 400 ft above the highest point of that structure. For recreational pilots under 49 USC 44809, the 400 ft AGL limit applies in controlled airspace; uncontrolled airspace permits flight up to 400 ft AGL under FAA-recognized Community Based Organization safety guidelines.
AGL also matters for weather: wind at 200–400 ft AGL is typically 30–50% higher than ground wind because surface friction slows the lower air layer. Drone manufacturers publish wind-resistance figures at sea level — they translate poorly to actual conditions at flight altitude.
What this means for pilots
Always think and plan in AGL, not MSL. Your drone's onboard altimeter typically shows AGL relative to takeoff point. When checking weather, prefer wind-at-altitude (200–400 ft) over surface wind. Altoa surfaces both.
FAQ
What's the difference between AGL and MSL?
AGL is height above the ground beneath you. MSL is height above sea level. A drone at 400 ft AGL on a Colorado mountaintop might be at 14,400 ft MSL.
Can I fly above 400 ft AGL near a tall building?
Yes — Part 107 allows flight up to 400 ft above the highest point of a structure, within 400 ft horizontally of it. Useful for tower inspection.
Does my drone show AGL or MSL?
Almost all consumer drones show AGL relative to the takeoff point. If you fly off a cliff, the altimeter will read 'higher than ground beneath you' even though your AGL relative to ground beneath the drone is much greater.
Related terms
FAA regulations change. Verify current rules at faa.gov/uas before relying on this article for flight planning. Altoa is not the FAA.