The acidity constant, pKa, of bromophenol blue (BPB) and phenol red (PR) indicators was determined by solution scanometry as a new, simple, fast and inexpensive method. The method is based on scanning of the cells containing the indicator solution with a scanner and then the color of each cell is analyzed with software written in visual basic (VB 6) media to red, green and blue values. The cells were built by creating holes in the Plexiglas® sheet. In addition, the acidity constants of the cited two indicators were determined spectrophotometrically. Hypspec program has been developed for the calculation of pKa values based on spectrophotometric data. Bromophenol blue and phenol red structures are similar and two pKa were found attributed to the phenolic groups. The agreement between the acidity constants calculated by solution scanometry, spectrophotometric method and values reported in the literature demonstrates the utility of the method here used. In addition, the Hyss2009 program was used for drawing of the corresponding distribution diagrams.