The purpose of this study is to develop a scale to measure fifth grade students' mathematical calibration skills. Besides, it aims to determine students' calibration skills through this scale. Results of the study revealed that fifth-grade students (n = 94) enrolling to study, have a medium-high level of (M = 55.12, SD = 21.76) mathematical calibration skills. Furthermore, the results showed that students' mathematical calibration skills do not show significant differences with respect to their gender (t = 0.501, p greater than 0.01). However, students' calibration skills show significant differences when considering their level of mathematics achievement (F[subscript (2-91)] = 69.46, p less than 0.001, [mu][superscript 2] = 0.60). In addition, a positive and significant relationship was found between students' mathematical calibration skills and their mathematics achievement (r = 0.85, p less than 0.001).