A method for determining a torque of an auger of a pile driving rig, wherein the pile driving rig comprises an auger rotator including a frame of the auger rotator, a driving motor, a frame of the driving motor and a lever arm, wherein the method comprises determining the torque of the auger by measuring at least one of the following items in structures of the pile driving rig: a force effected by the torque on at least one point in the structures of the pile driving rig, or an elongation caused by the force effected by the torque on at least one point in the structures of the pile driving rig, or a strain caused by the force effected by the torque on at least one point in the structures of the pile driving rig, or a deformation caused by the force effected by the torque on at least one point in the structures of the pile driving rig; as well as by calculating the torque of the auger from a measurement result thus obtained, wherein the force to be measured for determining the torque is a supporting force between the frame of the driving motor of the auger rotator and the frame of the auger rotator, and said supporting force is measured by a force sensor placed in the lever arm placed between the frame of the driving motor of the auger rotator and the frame of the auger rotator. wherein the pile driving rig comprises an auger rotator including a frame of the auger rotator, a driving motor, a frame of the driving motor and a lever arm, wherein the method comprises determining the torque of the auger by measuring at least one of the following items in structures of the pile driving rig: a force effected by the torque on at least one point in the structures of the pile driving rig, or an elongation caused by the force effected by the torque on at least one point in the structures of the pile driving rig, or a strain caused by the force effected by the torque on at least one point in the structures of the pile driving rig, or a deformation caused by the force effected by the torque on at least one point in the structures of the pile driving rig; as well as by calculating the torque of the auger from a measurement result thus obtained, wherein the force to be measured for determining the torque is a supporting force between the frame of the driving motor of the auger rotator and the frame of the auger rotator, and said supporting force is measured by a force sensor placed in the lever arm placed between the frame of the driving motor of the auger rotator and the frame of the auger rotator. a force effected by the torque on at least one point in the structures of the pile driving rig, or an elongation caused by the force effected by the torque on at least one point in the structures of the pile driving rig, or a strain caused by the force effected by the torque on at least one point in the structures of the pile driving rig, or a deformation caused by the force effected by the torque on at least one point in the structures of the pile driving rig; as well as by calculating the torque of the auger from a measurement result thus obtained, wherein the force to be measured for determining the torque is a supporting force between the frame of the driving motor of the auger rotator and the frame of the auger rotator, and said supporting force is measured by a force sensor placed in the lever arm placed between the frame of the driving motor of the auger rotator and the frame of the auger rotator.