Springer International Publishing Switzerland 2017. This paper investigates the modeling of elongation in plastic fiber ropes for cable-driven parallel robots. The aim is to increase the accuracy of such amachine by incorporating a simple model for cable elongation when a force is applied. Several other modeling techniques already exist which take into account pulleys, cable mass, and the cables' Young's modulus. Their calculation is involved and accuracy improvements are yet to be verified completely. Here, a simpler model which only takes into account a theoretical force, based on robot geometry, at a given pose and measured elongation coefficients is proposed. It is implemented and verified experimentally, on the fully constrained IPAnema 3 prototype. It is shown to give an accuracy improvement of two fifths, from 46.5mm to 29.0mm average position deviation.