By comparison, core loss is relatively straightforward for most applications, and we rely on data collected by the manufacturers to predict the performance. This data is usually adequate as long as all of the variables are taken into account. In this article, we address the seemingly simple task of modeling the empirical data for ferrite cores with equations. It can get quite involved, but the results can be very powerful and useful for CAD design programs. Most manufacturers have not gone very far with this approach, and we are still required to use curves to get the results we need.