A method for calculating an ocular distance is presented. The method includes the following steps. A three-dimensional (3D) image display device generates one or more second display points and displays one or more virtual reference points. One or more calibration points are obtained, and these calibration points are generated through interaction by a user using an interaction component with the reference points. An ocular distance of the user is calculated according to a relative position between the display points, the calibration points, and the user.
