This study aimed to evaluate Root ZX accuracy with different NaOCl concentrations and to observe effects of the alginate model when NaOCl was used in the canal during electronic measurements. Fifty extracted single-rooted, single-canal human teeth were used in five experimental groups. NaOCl concentrations of 5.25%, 2.65%, 1.00%, and 0.50%, respectively, were injected into the root canals of teeth in four groups and distilled water in control group 5. After measuring root lengths with Root, the files were locked in place. There were no statistically significant differences among all the groups (p > 0.95) when evaluating the distance of the file tips and apical constriction or for the distance from file tip to apical foramen. Root could be used in root canal length measurements with various NaOCl concentrations. Designation of apical constriction needs more care. The alginate model could be used for in vitro electronic measurements with various NaOCI concentrations.