Absolute depths are not required for well completion, but they certainly are for establishing field maps. Measuring depths with logging cables has been done either by determining the length of cable going over a sheave or by determining the length of cable magnetically marked under a known tension and hanging in the borehole. The second technique seems to be universally used today. However, the correction procedure to account for the stretch is not disclosed by the logging companies, and no industry standard has been established to date, In this work, the mechanical characteristics of the most common cables are summarized, and stretch theories are developed. The cases of both a standing tool and a moving tool are examined in a vertical borehole. The algorithms are developed assuming both a chain-like behavior and a rod-like behavior of the cable. The results are given in the form of tables and graphs. The cases of slanted boreholes without doglegs or curvature are also presented.