Background and Aims: Acurate measurements of variables are crucial in epidemiological studies. Therefore, even the best design cannot prevent bugs caused due to the lack of reliability and validity measurement in studies. The aim of this study is to determine the validity of teeth-canal measurement.

Materials and Methods: This methodological study used available data of patients referred to dental clinics at Hamadan University of Medical Sciences in Hamadan with sample size or 58 cases in 2012. In order to determine the reliability of measuring the length of canals and introduce the most appropriate measure met of the actual data, Bland-Altman plot and intraclass correlation coefficient (ICC) were used and finally compared.

Results: In this study, the mean ± SD of channel length in the apex locator Root ZX were 21.93 ± 2.28 mm and in X-ray PA were 22.4 ± 2.38 mm. ICC between the length of canals by the apex locator and radiographic in all teeth was 0.989. Bland-Altman plot showed that absolute agreement between the two methods of measurement.

Conclusion: The findings of this study ensure dental professionals that measuring the length of channels by PA method is more practical and easier and prove different approaches of the reliability and validity. However, we recommend using ICC and Bland Altman methods due to their informative nature and consideration of absolute agreement instead of consistency.