During the design of reinforced concrete elements, satisfying serviceability limit state conditions is very important. To simplify the calculations of crack width, for the elements subjected to bending, the EN 1992-1-1 (2013) gives a restriction of bar diameter or bar spacing which satisfy allowable crack width (tables 7.2(N) and 7.3(N)). During the last decades, FRP reinforcement became a good replacement for steel reinforcement, especially in an aggressive environment. Calculation methods for reinforced concrete elements with FRP bars (FRPRC) are developed from calculation methods for reinforced concrete elements with steel bars. Now, more and more, these rules are implemented in some national codes, and they will be implemented in Eurocodes soon. Procedures for the calculation of maximum bar diameter and bar spacing to control crack width are shown in the paper. These two values depend on each other and the focus of the paper is set on calculations of the bar diameter. Due to different modulus of elasticity between FRP and steel, the tables used for steel cannot be used for concrete beams reinforced with FRP bars. Therefore, the parametric calculations of maximum FRP bar diameter are described in this paper and new tables and diagrams are shown. The calculations were made according to rules from EN 1992-1-1 (2013), paragraph 7.3.4 and Eqs. (7.8) and (7.9) but instead of the material properties for steel reinforcement, those for FRP reinforcement are used. For additional explanations and considerations, EC2 Commentary (2008) is used. Also, due to many types of FRP reinforcement, one table for different materials will not be sufficient. Therefore, for easier usage, diagrams for maximum value of bar diameter are developed and shown in the paper.