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, 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; wherein the hopper comprises a first reference element, which, in use, is placed in contact with the stack of blanks, establishes a position reference for the blanks of the stack of blanks, is, relative to the frame, in the same position regardless of the format of the blanks and, hence, is not moved, relative to the frame, due to a format change operation, the feeding unit is characterized in that: the hopper is configured to contain blanks each comprising: two longitudinal folding lines, a plurality of transverse folding lines defining, between the two longitudinal folding lines, a plurality of panels, two first wings, which are connected to a first longitudinal folding line and delimit, between one another, an empty space with a triangular shape and having a vertex in the area of the first longitudinal folding line, and two second wings, which are connected to a second longitudinal folding line; and the first reference element is placed and shaped in such a way that the position reference is located in the area of the vertex of the empty space defined between the two first wings of each blank. 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, 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; wherein the hopper comprises a first reference element, which, in use, is placed in contact with the stack of blanks, establishes a position reference for the blanks of the stack of blanks, is, relative to the frame, in the same position regardless of the format of the blanks and, hence, is not moved, relative to the frame, due to a format change operation, the feeding unit is characterized in that: the hopper is configured to contain blanks each comprising: two longitudinal folding lines, a plurality of transverse folding lines defining, between the two longitudinal folding lines, a plurality of panels, two first wings, which are connected to a first longitudinal folding line and delimit, between one another, an empty space with a triangular shape and having a vertex in the area of the first longitudinal folding line, and two second wings, which are connected to a second longitudinal folding line; and the first reference element is placed and shaped in such a way that the position reference is located in the area of the vertex of the empty space defined between the two first wings of each blank. the hopper is configured to contain blanks each comprising: two longitudinal folding lines, a plurality of transverse folding lines defining, between the two longitudinal folding lines, a plurality of panels, two first wings, which are connected to a first longitudinal folding line and delimit, between one another, an empty space with a triangular shape and having a vertex in the area of the first longitudinal folding line, and two second wings, which are connected to a second longitudinal folding line; and the first reference element is placed and shaped in such a way that the position reference is located in the area of the vertex of the empty space defined between the two first wings of each blank.