This chapter determines stellar properties from seismic data. It discusses how the average seismic properties discussed in the previous chapters are used in determining the mass and radius of a star. The chapter provides two ways of determining stellar properties: the “direct method” and grid-based modeling. The first method produces a set of model-independent results derived from a set of equations. On the other hand, the grid-based model, which can make up for the shortcomings of the direct method, derives its results from a fairly dense grid of stellar models of different metallicities that cover a wide range of masses and evolutionary stages.