Purpose: To compare two methods used by novice and expert operators for selecting interdental brush (IDB) size for periodontitis patients: (1) sequential testing or (2) using a color-coded taper tip device (CTD) corresponding to color-coded brush sizes. Methods: Six operators, one experienced and five dental students, employed both methods to determine the IDB with best fit for 204 interdental spaces in 34 periodontitis patients. The percentage of agreement and the inter-methods reliability was evaluated. The influence of anatomical features on differences between the operators or method was also investigated. Results: Moderate to substantial correlation was found between the two methods but the reliability was stronger when different operators used the same method, irrespective of the method, than when they used a different method. Among the anatomical factors studied, only sites in molar regions were associated with significant differences. Clinical significance: Use of a dedicated color-coded taper tip may be an alternative to the fastidious sequential testing of different IDB in selecting best-fit IDB diameter for periodontal patients with moderate to broad interdental spaces.