The Box and Blocks Test (BBT) is a widely used outcome measure for manual dexterity assessments in neurological rehabilitation. The BBT score is based on the maximum number of cubes that a person is able to displace during a 60s time window. In this paper, a low-cost instrumented system to automatically obtain the number of cubes using proximity sensors is presented. For that purpose, the central partition of the BBT was sensorized, aiming to minimise the employed sensors and minimally alter the physical BBT box. The counting system, connected to the mobile app, allows for the self-administration of the test as users only need to follow the presented instructions. Firstly, the methodology used to automate the test scoring is presented, including the sensors’ description and the prototype design. Then, the obtained success rate in cube counting is shown, with an average of 98% in trials with five healthy users. Finally, the conclusions and future work are shown. The results support the use of automated methods for upper limb assessment, providing more objective results and additional information about user performance.