Outside Mount

• 1). Measure the height of the window from the top of the window frame to the base of the windowsill to determine the length of the blind.
  
  
• 2). Measure straight across the front of the window from the outside of the left edge of the frame to the outside of the right edge. Add three-quarters of an inch to each side for adequate overlap to determine the width of the blind.
  
  
• 3). Add extra length to your measurements if you wish to mount the blind higher than the frame or you want it to extend farther beyond the base of the window. Add extra width if you want the blind to extend farther past the sides of the window. This technique can add extra protection against sunlight. It can also cover damaged walls and create the impression of a larger window.
  
  

Inside Mount

• 1). Measure the inside of the window frame from the top inside edge to the top of the sill to find the necessary length for your blind.
  
  
• 2). Measure the width of the window in three separate places to determine how wide the blind should be. Most windows are not framed completely square, and the width will vary from top to bottom. Measure from the inside of the left edge of the frame to the inside of the right edge at the top, middle, and bottom of the window. Use the narrowest width for your blind measurement.
  
  
• 3). Deduct a quarter of an inch from your final measurements if you don't want the blind to extend to the sill or to touch the edges of the window. Round down fractions to the nearest inch -- with an inside mount, rounding up might cause the blind not to fit inside the window frame.