Generally most standard barn doors are approximately 36 x 84 or 42 x 80 with enough extra lip to overlap most standard door frames 36 x 80 by an inch or so.
Barn door height.
For instance if you have a doorway that s 35 you ll want a track that s at least 70 although a safe 6ft.
Most barn door sizes fall anywhere between 36 wide on the shorter side by 96 tall on the longer side.
Measure from outside to outside of casing molding.
Measure across for the width and from the top of the casing molding to the floor for height.
Add 1 to 2 per door for overlap depending on privacy needs.
For the door height we recommend measuring from the floor to the top of the casing.
72 would probably be even better.
Barn door measuring guide for door openings with casing molding.