It's completely variable in airspeed/altitude and density altitude. GVW is also a major consideration!
How does autorotation work in a helicopter?
Autorotation is a state of flight in which the main rotor system of a helicopter or similar aircraft turns by the action of air moving up through the rotor, as with an autogyro, rather than engine power driving the rotor. ... It is the means by which a helicopter can land safely in the event of complete engine failure.
