Three-dimensional hysteretic phenomena for sputtered Co-Pt thin film permanent magnet material of moderate coercivity are accurately predicted using only microstructural properties as input data. The Co-Pt material is novel in that it exhibits an exceptionally high energy product (BH)max up to 7.1 MG Oe, given certain fabrication constraints imposed by the device application. The 5000 Å thick sample described here consists of perpendicularly oriented grains approximately 560 Å in diameter grown on a 1000 Å Cr underlayer. The polycrystalline Co-Pt film exhibits [10·1] oriented hcp texture with the c-axis directed at an angle of 28° from the film plane and with its planar projection randomly distributed in all directions. The theory includes complete magnetostatic interactions, incoherent rotation of magnetisation within grains, and exchange interactions as suggested by the granular structure. Fitting to an experimental torque curve shows that the crystalline anisotropy within the grains is 4.0 × 106 erg/cm3. Theoretical longitudinal coercivity is 2400 vs. 2200 Oe experimentally; theoretical perpendicular coercivity is 2400 vs. 2800 Oe experimentally. Hysteresis loop shapes, including the squareness and maximum energy product, are also accurately predicted.