Disc loading is the ratio of aircraft weight in hover to the total rotor disc area, the area swept by the blades. In fluid dynamics it is the average pressure rise across the actuator disc. Simple momentum theory shows that, for a given weight, a larger disc moves more air more slowly, so the induced velocity falls and the ideal hover power falls too. Low disc loading therefore gives better hover efficiency, lower downwash and noise, but needs larger rotors.
Typical values depend on the vehicle type. Helicopters sit at roughly 14 to 72 kg/m2 (3 to 15 lb/ft2) in the reference data, from a light Robinson R22 up to the CH-53E, while a tiltrotor such as the MV-22B reaches about 130 kg/m2. Multirotor drones and eVTOL aircraft with many small rotors usually fall between helicopter and tiltrotor values.
On a datasheet it is given in kg/m2 or lb/ft2, calculated at maximum take-off weight and the total disc area. Some documents use the term power loading (thrust per unit power) next to it.
A frequent mistake is dividing weight by the area of the fuselage or by one rotor only, or counting overlapping or ducted discs inconsistently. Another is comparing disc loading at different weights: figures at maximum weight and at typical mission weight are not equivalent. Disc loading also should be read together with power loading and hover figure of merit, not alone.
