A measuring adapter (1) for a measuring instrument for use in connection with hip prosthesis surgery is provided. The measuring adapter (1) comprises a measuring head (2) and a connector (3)； the measuring head (2) comprises a front end (2a), a rear end (2b) and an upper surface (4a). The upper surface (4a) is convex. The measuring head (2), along an axial direction of the measuring adapter (1), further comprises a central through-going bore (5) adapted to receive an actuating rod (8). The measuring head (2) is adapted to expand from a relaxed state to an expanded state when the actuating rod (8) is axially displaced in the central through-going bore (5)； and the measuring head (2) is divided into at least two separate sections (6). The connector (3) is hollow and slotted at one end in axial direction of the measuring head (2) into a number of legs (7), the number of legs (7) corresponding to the number of the at least two separate sections (6) of the measuring head (2). The legs (7) of the connector (3) are each connected to one of the at least two separate sections (6) of the measuring head (2) on the rear end (2b) of the measuring head (2). A securing arrangement (18) is provided at the opposite end of the connector (3) relative to the connection to the measuring head (2), and at least a part of the upper surface (4a) of the measuring head (2) is adapted to, in one expanded state, adopt the shape of a spherical cap or a convex shape comprising at least a spherical segment. A measuring adapter (1) is also provided that comprises windows or through-going holes (10) or windows.
