Extended or modified release formulations are becoming more and more common within the pharmaceutical industry due to their advantages for patient compliance and efficacy. Manufactured using fluid bed coating, the process is typically controlled by spraying a fixed quantity of release coating on the drug loaded substrate as a means of achieving the desired dissolution profile. In this work a control method is explored whereby real-time size measurements of the in-process particles are used to gauge the true thickness of the release coating, and thereby determine when the end of spraying has been reached.