Bi-level blade of a lawnmower comprises a central portion lying on a first horizontal geometrical plane, a center of the central portion is keyed to a vertical motor axis which identifies a direction of rotation of the bi-level blade, said direction of rotation lies on said first horizontal geometrical plane, said bi-level blade extends a longitudinal length from the center of the central portion extending outwardly along a longitudinal axis, said longitudinal axis is perpendicular to the direction of rotation and lies on the first horizontal geometrical plane, from the central portion towards both outward directions along the longitudinal axis extending a upper outward portion and a lower outward portion of the bi-level blade, said upper outward portion comprises an upper cutting edge facing to a front of the direction of rotation, said upper cutting edge comprises an outward end, at least said outward end lies on an upper horizontal geometric plane which is higher by a first vertical distance with respect to said first horizontal geometrical plane, said first vertical distance is measured along a vertical axis which is parallel to the vertical motor axis, said upper cutting edge is adapted to cut an upper portion of a blade of grass, said lower outward portion comprises a lower cutting edge facing to the front of the direction of rotation, said lower cutting edge comprises an outward end, at least said outward end lies on a lower horizontal geometric plane which is lower by a second vertical distance with respect to said first horizontal geometrical plane, said second vertical distance is measured along the vertical axis, said lower cutting edge is adapted to cut a lower portion of a blade of grass, said lower cutting edge is set back by a transverse distance with respect to said upper cutting edge, wherein said transverse distance is measured along a transversal axis, said transversal axis lying on the first horizontal geometrical plane and it is perpendicular to the longitudinal axis, a vertical distance of separation between the outward end of the upper cutting edge and the outward end of the lower cutting edge is the sum of the first vertical distance and of the second vertical distance, said vertical distance of separation identifies an opening between the upper outward portion and the lower outward portion, said opening is adapted to allow an air flow coming from the front of the direction of rotation to pass through, said lower outward portion comprises a rear outward portion facing to the rear of the direction of rotation in direction of the transversal axis, said rear outward portion is bent upwards in direction of the vertical axis so as to be adapted to direct a part of the air flow upwards in direction of the vertical axis, an upper end of the rear outward portion is elevated by a third vertical distance above the upper horizontal geometric plane, said upper outward portion comprises a rear outward portion facing to the rear of the direction of rotation in direction of the transversal axis, said rear outward portion reduces a transverse length of the upper outward portion, said upper outward portion is shorter by a longitudinal length with respect to said lower outward portion, said longitudinal length is measured along the longitudinal axis between said outward end of the upper cutting edge and said outward end of the lower cutting edge, a first axis between the center of the central portion and the outward end of the upper cutting edge is inclined by a first angle (α) with respect to the longitudinal axis as that the upper cutting edge is off axis with respect to the longitudinal axis, a second axis between the center of the central portion and the outward end of the lower cutting edge is inclined by a second angle (β) with respect to the longitudinal axis as that the lower cutting edge is off axis with respect to the longitudinal axis, said bi-level blade is a single piece, said outward end of the lower cutting edge of the lower outward portion extends by a second transverse length from the longitudinal axis towards the front of the direction of rotation in direction of the transversal axis, said upper cutting edge of the upper outward portion extends along the longitudinal axis in direction inward to the bi-level blade for the entire longitudinal length of the upper outward portion, said central portion comprises a central cutting edge facing to the front of the direction of rotation, said central cutting edge comprises an inward end and an outward end lying on the first horizontal geometrical plane, said inward end of the central cutting edge is located on the front of the center of the central portion, a frontal median portion of the bi-level blade which links together the central portion and the upper outward portion, comprises an upper median cutting edge facing to the front of the direction of rotation, said upper median cutting edge comprises an inward end and an outward end, said inward end is in contact with said outward end of the central cutting edge, said inward end of the upper median cutting edge lies on the horizontal geometric plane, said outward end of the upper median cutting edge is in contact with an inward end of the upper cutting edge.