The present invention relates to a method for measuring the liquid-metal surface level (13) and the slag surface level (14) in the crucible (1) of a metallurgical shaft furnace comprising the following steps: measuring, at one or more points on the external wall (2) of the crucible, the following variables: the circumferential strain in said external wall (2) by means of a number of strain-gauge sensors (6) fixed to the armor (4) of the external wall (2) of the crucible; and the temperature of said external wall (2) by means of one or more temperature sensors (7) fixed to the armor (4) of the external wall (2) of the crucible; introducing said variables measured at a number of points on the external wall of the crucible into the general equation governing circumferential strain, the solution of which is analytical, and which contains two unknowns, the liquid metal level and the overall liquid metal/slag level, considering set parameters; and solving said equation and obtaining an analytical solution giving the liquid metal surface level (13) and the slag surface level (14) in the crucible (1).