The authors present a new method to reliably measure the length of the mid-portion of the calcaneus. The authors defined the "mid-calcaneal length" as the line connecting the high point of the convex arc of the posterior subtalar joint facet and the low point of the concave arc of the calcaneocuboid joint. Statistical analysis of 810 measurements taken by 6 observers confirmed high intraobserver reliability, interobserver reliability, and internal consistency (Cronbach coefficient α = .98) and low error rate (Pearson correlation coefficient = .0001). The authors have used this measurement as a tool to determine the change in calcaneal length after osteotomy lengthening procedures and present it as a tool for clinical practice and research.