Among the knowledge required by healthcare professionals to manage pain is an understanding of the differences between opioid agents and formulations. As the list of new opioid formulations continues to grow, it is increasingly important that clinicians understand the basic pharmacology of these analgesics and how to calculate equianalgesic doses. Administering an equianalgesic dose increases the likelihood that the transition to another opioid or route will be tolerated without loss of pain control or excessive side effects. Although calculation of equianalgesic doses requires relatively simple mathematical skills, few clinicians are prepared to compute them. The purpose of this article is to provide a basic review of the pharmacology of opioids, explain how to calculate an equianalgesic dose, and briefly describe some of the current controversies of the relative potencies of opioids listed in equianalgesic tables.