Total Hip Arthroplasty (THA) is a procedure where a defective hip joint with pain symptoms or functional impairment is replaced by a hip prosthesis. During this procedure, the optimal hip prosthesis should be chosen and placed in the correct orientation to achieve a stable hip joint. Failure to do so can lead to dislocation, mechanical failure or infection of the hip joint. To improve the outcome of the THA, range of motion (ROM) of the hip joint can be evaluated during the surgery after placement of the hip prosthesis. Current methods of measuring hip ROM have some limitations. For example, there is a low intra- and inter-test reliability between identification of the bony landmarks and goniometric alignment. The goal of this project was to develop an instrument that can measure the ROM during THA without the limitations of current instruments. An instrument was developed that determines its orientation via an inertial measurement unit (IMU). The IMU is connected on the upper leg via a strap and aligned with the bony landmarks via laser beams. A test has been performed to validate the usage of the instrument. The ROM of the hip for flexion and abduction motion was measured with the instrument and compared to a reference measurement made with two video cameras. A significant difference was found: the instrument did not stay aligned with the hip joint. For further development of the instrument, the drift should be minimised and multiple straps should be tested to allow a better fixation. Additionally, the added-value of the laser requires further research.