FIELD : medicine.SUBSTANCE : invention relates to medicine. Pattern for determining the size of the femur implant of the knee joint endoprosthesis suitable for the patient contains the main body, probe element, two mating parts for fit and basic attachment, respectively, to the central and lateral anterior condyles of the patient' s distal femur and at least one scale bar and an associated arrow for indicating the position of the probe element in the measuring direction with respect to at least one of the mating parts for indicating a suitable implant size. Probe element, moving relative to the main body along the direction of measurement, contains a probe with a probe tip to fit the posterior base point of the patient' s distal femur. These mating parts are installed with the possibility of movement with respect to the main body thus, that the distance from the tip of the probe to these mating parts, projected onto this direction of measurement, is established for these mating parts in such a way that this distance is different with respect to these mating parts. Each matched part has its own scale bar and an arrow related to it to indicate the position of the probe element in the direction of measurement with respect to the corresponding mating part and for the appropriate implant size resulting from this indication. There is a connection between the mating parts, which, with the relative movement of one mating part relative to the main body, entails a relative movement and the other mating part relative to the main body.EFFECT : invention provides for the prevention of measurement errors.9 cl, 9 dwg