Inside Mount Measure the inside opening width on top, middle and bottom. Choose the smallest value as the opening width to place the order. Measure the inside opening height on left, middle and right. Choose the largest value as the opening height to place the order. We will take off 0.4 inch based on opening width to make the blind. Shade height will be same as the opening height. Outside Mount Measure the outer frame width and add 1-3 inches as the final blind width to place the order. Measure the outer frame height and add 3-5 inches as the final blind height to place the order. We will make NO changes on the final blind size you chose.