Always measure with a steel tape. Never use a cloth tape. Measure sizes to the nearest eighth of an inch (1/8"). Don't be surprised if your windows are not perfectly square. Most aren't. You probably won't notice.
On your notes clearly indicate which measurement is the width and which is the height. It is very common to transpose measurements. Try to always measure the width first, then height.
INSIDE MOUNT (recessed within your window opening)
We recommend an Inside Mount whenever possible for a neater look. When you specify an inside mount, provide us the EXACT window opening size. DO NOT TAKE A DEDUCTION!
Manufacturers will automatically deduct approximately 3/8" to 1/2" so your products will operate properly and not rub against your window frame.
FOR WIDTH, measure in three places and use thenarrowest width.
FOR HEIGHT, measure in three places and use the longest measurement for all products EXCEPT FOR vertical blinds and privacy sheer blinds (sometimes referred to as window shadings) such as WhisperShades (use the shortest height for these).
OUTSIDE MOUNT (mounted on your molding or drywall)
Outside mounts hang outside the window opening either on the wood frame or above and beyond the wood frame. That will make your window appear bigger and hide unattractive windows. Outside Mounts are necesssary whenever your window openings are too shallow to place a window covering. To ensure minimum light gaps and maximum privacy, add 4 to 5 inches on each of the four sides. Leave room for the mounting brackets, which can be 1 to 3 inches tall.
For outside mounts, specify the exact width and exact height you want the product to be. We will make your product the exact size you specify and we will not take any deductions. So you must add to the window opening measurement to allow for mounting brackets and the distance you want to go past the window.