Measure the window's width. If existing mini blinds are in place, be certain to note the gap or overlap of the blinds at each side.
Measure the height of the window opening. Be sure to include a minimum 3 inches extra for wall mounted blinds to allow for the mounting at the top above the window opening to insure full coverage when the mini blinds are fully extended.
Measure the depth of the window jamb from the outer edge to the face of the sash. For mini blinds that are to be mounted within the window opening and you are planning on the same type of arrangement, the depth of the jamb space must be determined to insure enough clearance and room for the mounting hardware.
Note the window type. There are a variety mounting options available for different types of windows. This information will help you and your retailer choose the appropriate style of mini blinds for your application.