Regulations

14 CFR Part 107, which sets the rules for commercial and most non-recreational operation of small unmanned aircraft systems.

A small unmanned aircraft weighs less than 55 pounds on takeoff, including everything on board or otherwise attached, such as payload.

The small unmanned aircraft and its associated elements, such as communication links and the control station, that are required for safe and efficient operation in the National Airspace System.

Yes. The weight is measured at takeoff and includes anything on board or otherwise attached to the aircraft, such as payload and accessories.

400 feet above ground level (AGL), unless the aircraft is flown within a 400-foot radius of a structure, in which case it may go up to 400 feet above that structure's immediate uppermost limit.