Background: Ankle joint dorsiflexion range of motion is essential to normal gait. Ankle equinus has been implicated in a number of foot and ankle pathologies included Achilles tendonitis, plantar fasciitis, ankle injury, forefoot pain, and foot ulceration. Reliable measurement of ankle joint dorsiflexion range of motion, both clinically and in a research setting, is important. Methods: The primary aim of this study was to investigate the intertester reliability of an innovative device for measuring ankle joint dorsiflexion range of motion. A total of 31 (n = 31) participants volunteered to take part in this study. A paired t-test was performed to assess for systematic differences between the mean measures of each rater. Intertester reliability was evaluated using the intraclass correlation coefficient (ICC) and their 95% confidence intervals. Results: A paired t-test demonstrated that the mean ankle joint dorsiflexion range of motion did not significantly differ between raters. The ankle joint ROM mean for rater 1 was 4.65 SD (3.71) and rater 2 was 4.67 SD (3.91). Intertester reliability for the use of the Dorsi-Meter was excellent and demonstrated a very narrow range of error. The ICC (95%CI) was 0.991 (0.980 to 0.995) the SEM (in degrees) was 0.07, the MDC95, in degrees was 0.19 and 95% LOA, degrees was –1.49 to 1.46. Conclusions: We found the intertester reliability of the Dorsi-Meter to demonstrate higher levels of intertester reliability compared to previous studies investigating other devices. We reported the MDC values to provide an estimate of the smallest amount of change in the ankle joint dorsiflexion range of motion that must be achieved to reflect a true change, outside the error of the test. The Dorsi-Meter has been established as an appropriate reliable device to measure ankle joint dorsiflexion for clinicians and researchers with very small minimal detectable change and limits of agreement.