Abstract: A method for capturing a size of an installation space for a door/window using remote image includes providing an installation space for a door/window having an edge, disposing a size-calibrating member at one side of the edge of the installation space for the door/window, using an image capturing device to acquire an image that contains with the installation space for the door/window and the size-calibrating member, transmitting mentioned image to an image measurement system, using the image measurement system to analyze the image and determine an image ratio between the installation space for the door/window and the size-calibrating member, and a practical size of the installation space can be figured out based on mentioned image ratio and a practical size of the size-calibrating member.