Measure from floor to top of trim (or cased opening if there is no trim). We recommend your door be 1" taller.
Measure from outside of trim to outside of trim (or cased opening if there is no trim). We recommend your door to be 3" wider if you have trim and 5" wider if you do not have trim.
Floor to Ceiling
Measure from floor to ceiling to ensure there is about 6" above the door opening to allow for hardware.
Will the door slide open to the left or to the right? Measure the wall space (including trim) on the side it will slide open. This should be at least as wide as the barn door you plan to hang.