Power requirement for steady movement of the load.
Output speed of the gear or gearmotor.
The overall efficiency of the driving unit ( gearbox ) and the driven unit efficiency ( such as the chain or belt stage efficiency etc. ).

See "Overall efficiency" calculation.
Torque Required at the Load
Variables   Units
PX Power hp
nL Rotational speed load rpm
ηT Overall efficiency %
TL Load torque lb-in