In a method of calculating a shift value of a cell contact, a reference region and a correction region may be set on an image of an actual cell block. The cell block may include a plurality of actual cell contacts formed using a mask. Each of preliminary shift values of the actual cell contacts with respect to target cell contacts in a target cell block to be formed using the mask may be measured based on the image. The preliminary shift values of the actual cell contacts in the reference region may be minimized. Actual shift values of the actual cell contacts in the correction region with respect to the minimized preliminary shift values may be calculated. Thus, the mask may be corrected using the accurately measured shift values so that the cell contacts may have designed positions.