Methods and apparatus for predicting viscosities of glass materials as a function of temperature and composition are provided. Two fitting parameters (fitting coefficients) are used for each of the viscosity-affecting components contained in the material. The parameters can accurately cover a wide range of temperatures (i.e., a wide range of viscosities) and a wide range of compositions. The viscosity predictions can be used as a guide for glass research as well as in feedback control systems for glass manufacturing processes. Methods and apparatus for predicting glass resistivity are also disclosed.