A method and a device for measuring the torque in the drivetrain (1) of a wind power plant is described, having at least two incremental encoders (7, 8) which are positioned at two different positions on at least one shaft (3) of the drivetrain (1) and which each supply periodic rotational signals, wherein the phases of the rotational signals are evaluated in order to detect a phase shift, and a torque of the shaft (1) is determined from the phase shift. The detected phase shift is corrected as a function of a zero load phase shift (AZero), using a rigidity factor K, wherein, in order to determine the zero load phase shift (AZero) and the rigidity factor K, in-situ calibration is carried out before and/or between the torque-determining processes. The in-situ calibration is performed at zero load of the wind power plant, i.e. below a rated rotational speed and with a generator torque equal to zero, and at the rated load of the wind power plant, i.e. at the rated rotational speed and with a generator torque greater than zero.