Linewidth measurements from 77–300°K and room temperature off‐resonance effective linewidth data at 9 GHz show that the microwave losses in ultra‐low‐loss Ca&sngbnd;V&sngbnd;In substituted YIG and Ca‐Ge‐In‐YIG are completely resolvable in terms of known processes and that only a small part of the loss is due to anisotropy broadening. For the lowest linewidth of 2 Oe observed to date (Ca‐Ge‐In‐YG), about 0. 5 Oe is due to rare earth impurities 0. 9 Oe is from porosity broadening, and 0. 2 Oe is from anisotropy. The remaining 0.4 Oe contribution is comparable to expected “intrinsic” single crystal linewidths.