A unit to feed blanks in a packer machine and comprising: a frame; a hopper, which is supported by the frame, is designed to hold a stack of blanks and has a pick-up opening, through which one blank at a time can be picked up from the stack of blanks; and a conveyor, which is supported by the frame and moves the blanks along a moving path, which ends in the hopper; wherein the frame comprises a support body, which is provided with a seat designed to house the hopper; and wherein, in order to contain blanks with different formats, the feeding unit can be adjusted by means of a format change operation, which entails changing the feeding unit from a first configuration, which is suited to contain a first format of the blanks, to a second configuration, which is suited to contain a second format of the blanks, which is different from the first format; the feeding unit is characterized in that: a plurality of different and interchangeable hoppers is provided, each associated with a corresponding format of the blanks; each hopper is fixed to the frame in a removable manner in order to be replaced during a format change operation so that the format change operation entails replacing a first hopper associated with the first format with a second hopper associated with the second format; and the support body is movable on the frame so as to move, during a format change operation, between a work position, in which the hopper housed in the support body is coupled to and aligned with the conveyor, and a replacement position, in which the hopper housed in the support body is uncoupled from and not aligned with the conveyor. a frame; a hopper, which is supported by the frame, is designed to hold a stack of blanks and has a pick-up opening, through which one blank at a time can be picked up from the stack of blanks; and a conveyor, which is supported by the frame and moves the blanks along a moving path, which ends in the hopper; wherein the frame comprises a support body, which is provided with a seat designed to house the hopper; and wherein, in order to contain blanks with different formats, the feeding unit can be adjusted by means of a format change operation, which entails changing the feeding unit from a first configuration, which is suited to contain a first format of the blanks, to a second configuration, which is suited to contain a second format of the blanks, which is different from the first format; the feeding unit is characterized in that: a plurality of different and interchangeable hoppers is provided, each associated with a corresponding format of the blanks; each hopper is fixed to the frame in a removable manner in order to be replaced during a format change operation so that the format change operation entails replacing a first hopper associated with the first format with a second hopper associated with the second format; and the support body is movable on the frame so as to move, during a format change operation, between a work position, in which the hopper housed in the support body is coupled to and aligned with the conveyor, and a replacement position, in which the hopper housed in the support body is uncoupled from and not aligned with the conveyor. a plurality of different and interchangeable hoppers is provided, each associated with a corresponding format of the blanks; each hopper is fixed to the frame in a removable manner in order to be replaced during a format change operation so that the format change operation entails replacing a first hopper associated with the first format with a second hopper associated with the second format; and the support body is movable on the frame so as to move, during a format change operation, between a work position, in which the hopper housed in the support body is coupled to and aligned with the conveyor, and a replacement position, in which the hopper housed in the support body is uncoupled from and not aligned with the conveyor.