Recent evidence suggests a correlation between spiral arm pitch angle and supermassive black hole (SMBH) mass. We use an improved method to accurately measure the spiral arm pitch angle in disk galaxies to generate quantitative data on this morphological feature for 34 galaxies with directly measured black hole masses. This method is compared with other means of estimating black hole mass to determine its effectiveness and usefulness relative to other existing relations. Such a relationship is predicted by leading theories of spiral structure in disk galaxies, including the density wave theory. We propose this relationship as a tool for estimating SMBH masses in disk galaxies, and have used this relation to construct a SMBH mass function for disk galaxies in the local universe.