The invention relates to a device (1) for measuring the width (B) and/or the position of a metal strip (2) or a slab, which has at least two measuring systems (3, 4), with each located on a side (5, 6) of the metal strip (2) or the slab, wherein each measuring system (3, 4) has a sensor (7) designed to detect the lateral end (8, 9) of the metal strip (2). To make the measuring device robust and to enable dynamic measurement, according to the invention the sensor (7) is located on a moving element (10) with which it can be moved in a straight line in a direction (Q) at right angles to the longitudinal direction (L) of the metal strip (2).