Blade for a rotary mower comprising - two cutter blades (3, 4) which are rotatable about the axis of rotation of the blade, which extend on both sides of the axis of rotation radially outwards in the direction of a longitudinal axis of the blade, - a cutting edge (6, 7) at a front edge (3a, 4a) of each cutter blade (3, 4) in the direction of rotation and - a guide device (11, 12) at a rear edge (3b, 4b) of each cutter blade (3, 4) in the direction of rotation which consists of a section of the cutter blade (3, 4) bent from the blade plane about a bending line (13a, 13b), wherein the bending line (13a, 13b) runs from an outer edge (3c, 4c) of the cutter blade (3, 4) to the rear edge (3b, 4b) thereof, wherein - each cutter blade (3, 4) has an outer section which over its entire extension in the direction of the longitudinal axis of the blade is broader than an inner section of the cutter blade (3, 4) adjoining the outer section, - the inner sections of the two cutter blades (3, 4) directly adjoin one another, - the sections on both cutter blades (3, 4) forming the two guide devices (11, 12) are bent upwards from the blade plane, - the outer sections and the inner sections of both cutter blades except for the two guiding devices (11, 12) lie in the blade plane and - the bending line (13a, 13b) of each of the two guiding devices and the longitudinal axis of the blade enclose an acute angle in a range from 10° to 15°, characterized in that - the upwardly pointing surfaces (11a, 12a) of the two guiding devices (11, 12) together account for at least 12 % and at most 20 % of the area of the entire upwardly pointing surface of the blade, - the cutting edge (6, 7) of each cutter blade (3, 4) extends exclusively along the front edge (3a, 3b) in the outer section of the cutter blade (3, 4) and - the bending line (13a, 13b) of the guide device (11, 12) of each cutter blade (3, 4) intersects the rear edge (3b, 4b) in the outer edge of the cutter blade (3, 4). - two cutter blades (3, 4) which are rotatable about the axis of rotation of the blade, which extend on both sides of the axis of rotation radially outwards in the direction of a longitudinal axis of the blade, - a cutting edge (6, 7) at a front edge (3a, 4a) of each cutter blade (3, 4) in the direction of rotation and - a guide device (11, 12) at a rear edge (3b, 4b) of each cutter blade (3, 4) in the direction of rotation which consists of a section of the cutter blade (3, 4) bent from the blade plane about a bending line (13a, 13b), wherein the bending line (13a, 13b) runs from an outer edge (3c, 4c) of the cutter blade (3, 4) to the rear edge (3b, 4b) thereof, wherein - each cutter blade (3, 4) has an outer section which over its entire extension in the direction of the longitudinal axis of the blade is broader than an inner section of the cutter blade (3, 4) adjoining the outer section, - the inner sections of the two cutter blades (3, 4) directly adjoin one another, - the sections on both cutter blades (3, 4) forming the two guide devices (11, 12) are bent upwards from the blade plane, - the outer sections and the inner sections of both cutter blades except for the two guiding devices (11, 12) lie in the blade plane and - the bending line (13a, 13b) of each of the two guiding devices and the longitudinal axis of the blade enclose an acute angle in a range from 10° to 15°, characterized in that - the upwardly pointing surfaces (11a, 12a) of the two guiding devices (11, 12) together account for at least 12 % and at most 20 % of the area of the entire upwardly pointing surface of the blade, - the cutting edge (6, 7) of each cutter blade (3, 4) extends exclusively along the front edge (3a, 3b) in the outer section of the cutter blade (3, 4) and - the bending line (13a, 13b) of the guide device (11, 12) of each cutter blade (3, 4) intersects the rear edge (3b, 4b) in the outer edge of the cutter blade (3, 4). - the upwardly pointing surfaces (11a, 12a) of the two guiding devices (11, 12) together account for at least 12 % and at most 20 % of the area of the entire upwardly pointing surface of the blade, - the cutting edge (6, 7) of each cutter blade (3, 4) extends exclusively along the front edge (3a, 3b) in the outer section of the cutter blade (3, 4) and - the bending line (13a, 13b) of the guide device (11, 12) of each cutter blade (3, 4) intersects the rear edge (3b, 4b) in the outer edge of the cutter blade (3, 4).