Measure TWICE to order ONCE. Don’t be surprised if your windows are not square.
Inside Mount or Outside Mount?
As a general rule, outside mounts are used for windows that do not have a definitive inside area, like a sliding glass door to the patio.
First, step back and decide whether you want the window treatment inside the window recess, or on the wall or molding. For an inside mount, the window must have enough unobstructed depth to accommodate the mounting. Be sure to include things like window locks, cranks, etc.
A flush inside mount is where the blind is completely recessed and none of it projects beyond the opening. Be sure to have enough depth for this type treatment.
Inside mounts are the usual recommendation since it provides a cleaner look.
Outside mounts makes a window appear larger, or can hide an unattractive window.
When you specify an inside mount, a deduction of up to ¼ inch is made to allow for operating clearance. For vertical blinds there is also a height deduction of ¼ inch. These adjustments are made so that the blind will not rub or scratch the window frame.
When you specify an outside mount, there will be no factory deductions, so you must add to allow for overlap and mounting brackets.