The invention relates to a length measuring device having a measuring slide, a linear guide in the form of a hollow profile, on which the measuring slide is mounted so it is externally displaceable, an inner slide, which is mounted so it is displaceable in the interior of the hollow profile, a magnet assembly, which magnetically couples measuring slide and inner slide, so that the inner slide follows every movement of the measuring slide along the hollow profile, a measuring unit for measuring the position of the inner slide, and a display, which is visible in the exterior of the hollow profile, of the length ascertained by the measuring unit in accordance with the measured position of the inner slide. The measuring unit has a sound source, a sound receiver, and a control and analysis unit connected thereto.
