The aim of this literature review was to examine definitions of medication calculation competence (MCC) based on studies on registered nurses. An integrative method was chosen for the review, summarising both the empirical and theoretical literature for the purpose of understanding medication calculation in terms of the competences involved. A total of 19 studies were included in the review. Based on this review, there is no shared understanding of the definition of MCC. The definitions of MCC found in the literature consist of five elements: 1) abstract thinking; 2) medication calculation from a nursing perspective; 3) mastery of mathematics; 4) equipment; and 5) personal qualities. MCC is a complex and multidimensional application of these elements both in connection with each other and as separate components.