Instrument for measuring dimensions, including: a mobile carriage capable of moving parallel to a guide, the guide defining a measuring axis; a driving device connected to the carriage by a transmission, so as to determine the linear displacement of the mobile carriage; a feeler attached to the mobile carriage and designed to come into contact with a part to be measured; a position transducer, arranged so as to supply a measurement of the feeler's position relative to the measuring axis; a piezoresistive force sensor for converting directly a contact force between the feeler and the part to be measured into an electric signal.