The CALPHAD (calculation of phase diagrams) approach is applied to predict the oxygen vacancy concentration at different temperatures and yttria concentrations of cubic yttria-stabilized zirconia (c-YSZ) single crystals. The quantitative mobility diagrams of oxygen ions are developed in a wide range of temperature and yttria concentration, using the experimental data from the literature. Therefore, the ionic conductivity of c-YSZ single crystals is predicted, using the mobility and oxygen vacancy concentration. Particularly, the conductivity of low-yttria c-YSZ is predicted by applying the CALPHAD approach for the first time. The conductivity prediction of low-yttria c-YSZ can be crucial, since new applications may be designed based on this new information. The activation energy and pre-exponential factor diagrams versus yttria concentration are also plotted.