Range of motion measurement is fundamental in the physical examination and functional evaluation of different joints. WIMUTM is an inertial device that allows the analysis of joint motion easily in real time. This study had a two-fold goal: (i) to evaluate the validity of WIMUTM on the measurement of different angle positions, compared with a standard goniometer and 2D video-based motion analysis software; and (ii) to evaluate the use of WIMUTM in the assessment of angulations in a joint, specifically assessing the validity and reliability of WIMUTM on the measurement of ankle dorsiflexion, compared to a standard goniometer and Kinovea. The intraclass correlation coefficient and Pearson´s correlation coefficient (r) were performed to calculate the concurrent validity, and Bland-Altman plots were performed to analyze agreement between measures. For the analysis of reliability, both relative and absolute indices were used. The results showed excellent validity and reliability of WIMUTM in the assessment of angle positions and ankle dorsiflexion. The current findings conclude that WIMUTM is a valid and reliable instrument to measure angle and joint motions. In short, WIMUTM provides a new clinical and sportive method of angle measurement.