Based on the window design, you have choice to mount your hard window covering mounted inside or outside the window casing. Please ensure to measure your windows carefully with a wooden, metal rule, or steel tape. Use of cloth tape is not recommended.
 
Factory tolerance for the width is +/- 1/8" & length is +/- 1/8".

Inside Mounts: Measure the inside width of the window opening at the top, middle and bottom. Measure the height inside the window opening at the left, right and center. Use the narrowest width measurement as Finished width and the shortest height measurement as the Finished Length measurement. Remember to always round your measurement to the nearest 1/8". The manufacturer will automatically deduct 1/8" on Finished Width & 0" deduction on Finished Length.
 
PLEASE DO NOT TAKE ANY DEDUCTIONS IN YOUR INSIDE MOUNT MEASUREMENTS.

Outside Mounts: Measure the desired width and height. To minimize light leakage, it's recommended that the shade over-lap the window opening at least 2" on each side and at the bottom.

Please Remember - "1/8” Accuracy" to your Measurements: Window measurements must be accurate within 1/8". With outside mounts, round your measurements up or down to the nearest 1/8". With inside mounts, always round down to the nearest 1/8". Rounding up could result in a shade that is too wide to fit within the window opening.