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 HOME > Technical Information > Measuring > Horizontal Blinds

Great Lakes Window Coverings - Blind Measuring

Measuring Horizontal Blinds

Things to Remember:

  • Use a steel tape for accuracy.
  • Measure the exact width of the window at 3 different places. Use the narrowest measurement and write it down. 
  • Measure the exact length from top of window opening to bottom sill. Use the shortest measurement and write it down
  • Make all measurements to the nearest 1/8 inch.
  • NOTE: All measurements should come from measuring the window. If you measure your existing blinds, the measurements will be incorrect.
  • Do not take your own deductions. The factory will take necessary deductions and allowances.
  • Double check all measurements.
  • Blinds may be mounted inside or outside the window casing. See below for specific instructions.
  • Vertical Blinds require special measuring considerations which are outlined below.
Inside Mount (see diagram below)

The window covering will hang inside the window frame. We recommend an inside mount whenever possible for a neater look. When you order, enter the exact dimensions of your window without making any allowances. The factory will take all necessary deductions for inside mounts. 

  1. Width: Width: Measure the EXACT distance across the window from the inside edge of the frame to the opposite inside edge in three places. Use the narrowest dimension.
  2. Height: Measure the EXACT distance from the top inside edge of the frame to the bottom inside edge of the frame in three places. Use the longest dimension for horizontal coverings, and the shortest for vertical coverings.
  3. Window Depth: The amount of space from the back of the window or obstruction to the windows outer edge (see below).
  4. See the Sill Depth Chart below for the minimum sill depth needed for installation and the minimum needed for the product to be flush with the front.


Flush Mount
  • 1.50" for 1" and 1/2" Mini Blinds, 3/8" Honeycomb Shades and Pleated Shades
  • 2.25" for 1" Wood Blinds and 3/4" Honeycomb Shades
  • 3.00" for 2" Aluminum Blinds and 2" Wood blinds
  • 4.75" for Vertical Blinds
Outside Mount (see diagram below)

The window covering will hang outside the actual window frame, over lapping the window frame for maximum privacy and light blockage. Please note that blinds require a flat surface for mounting. If you have a casement around your window, you may mount the headrail directly on the casement, but not on the wall outside of it. In order to make the width of the blind extend beyond the width of the casement, it is necessary to mount the headrail above the casement.

  1. Width: Measure the desired width. To minimize light leakage the shade should overlap the window opening by at least 2" on each side and at the bottom.  
  2. Height: Measure the  distance from the top outside edge of the window frame the bottom outside edge of the frame. If there is not a window frame add at least 2" inches on the top and the bottom to minimize light leakage.  The headrail on a wood or faux wood 2" blind is about 2 1/2" high. 
  3. Leave room for the mounting brackets, which are about 2-1/2" tall
  4. For Vertical Blinds see our Vertical instructions


If you have a measuring situation that was not covered here, it is most likely covered in the section called special measuring situations. In that section we cover French and sliding doors, curved windows and many other topics.

 HOME > Technical Information > Measuring > Horizontal Blinds

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