A method of determining the blocking position of an optical lens Method for determining a position of an optical lens member placed on a lens blocking ring (22), the method comprising: - a reference system providing step (S1), - a blocking ring data providing step (S2), - an optical lens member surface data providing step (S3), - a position parameters providing step (S4) during which position parameters defining a position of a reference point of the surface of the lens member with respect to the main plane of the reference system and an orientation, about the main axis of said placed surface at said reference point, - an initial position determining step (S5) during which the position of the placed surface is determined according to the position parameters, - a repositioning step (S6) during which the placed surface is virtually translated and rotated, - an altitude determination step (S7) during which a difference in position between the blocking ring and the placed surface is determined, the repositioning and altitude determining steps (S6, S7) are repeated so as to minimizing the difference in position between the blocking ring and the placed surface.