Yang XJ, et al. - In this investigation, researchers developed a mathematical model that could calculate the desired laminoplasty opening size (LOS) based on the target sagittal canal diameter (SCD) before single-door cervical laminoplasty (SDCL) taking into account the effects of surgical drilling. The 95% confidence intervals of SCD after the surgery were within the range of 14 mm and 14.5 mm according to the derived formula. The desired LOS could be calculated based on the target SCD by applying the mathematical model and derived formula, which could help the surgeon select an optimal mini-plate before SDCL. At the same time, for the convenience of the derived formula, a new measuring device called Lei's ruler is designed.