The paper reports about the development of an automatic tool that can be used to measure the depth of cracks with millimetric precision on board of a structural inspection robot. The system is based on two piezoelectric ultrasonic transducers with central frequency of 50 kHz that are utilized to take Time-of-Flight (ToF) ultrasound measurements across the crack to determine its depth. In order to cope with the intrinsic inhomogeneity of concrete, the measurement method adopted in the automatic system is based on the ...