From a numerically exact solution of the Master equation for hoppingtransport in a disordered energy landscape with a Gaussian densityof states, we determine the dependence on temperature, carrier density, and electric field of the charge carrier mobility. Experimentalspace-charge limited currents in semiconducting polymer-based devices are excellently reproduced with this unified description of the mobility. At room temperature it is mainly the dependence on carrier density that plays an important role, whereas at low temperatures andhigh fields the electric field dependence becomes important. Omission of the carrier-density dependence has led to an underestimation of the hopping distance and the width of the density of states in these polymers.