Recent years have seen a growing interest in hazelnut cultivation, justified by a doubling of the area cultivated with this crop since the year 2000. As a result, mechanization in this field, particularly with regards to harvesting machines, has also evolved significantly. Nevertheless, spread of electronics and telemetry systems only now has taken place, and there is a need to production mapping system. The aim of this work is to prototype and test a low-cost system for measuring the volume of harvested fruits using distance sensors. In detail, ultrasonic sensors have been employed connected to an Arduino microcontroller. Measured data have been acquired by serial communication and processed later using Matlab software. Several processing algorithms were tested in order to obtain more precise information about the volume occupied by fruits from the measured distances. Several tests were conducted by discharging hazelnut samples inside a sheet metal container that simulates on a small scale, the harvesting trailer. The container was provided with a lid, featuring holes for ultrasonic sensors fixing, and has been placed on 4 load cells, to monitor the weight of the hazelnuts during the tests. Measurements with ultrasonic systems show that the spherical shape of hazelnuts does not allow for high accuracy. However, the system allows adequate tracking of the filling status and distribution of hazelnuts in the trailer, and with the elimination of outlier data, it is possible to reduce the volume measurement error.