Analytical equations describing the three-dimensional field of permanent magnets are attractive tools for the optimization of permanent-magnet based structures. The shape of the magnets determines to a high extent the type of solution. The objective of this research is to find the equations describing the field of a pyramidal frustum, based on the Biot–Savart law. We develop analytical equations describing the field of current carrying sheets. These equations make it possible to treat the field of any permanent-magnet shape with a uniform magnetization and flat surfaces.