How To Measure For A Barn Door Size. Measure across for the width and from the top of the casing/molding to the floor for height. You have to begin at the left edge.
Similarly to the height measurement, to find out how wide your barn door should be, you should measure the door frame from one side to the other. (in this example the total width is 41″). The width of your opening, the height of your opening from the floor to the top of the opening, the space between the top of the opening to the ceiling, and the width of the right and left walls of your opening.
To figure out what size track you need, double your final width measurement.
Measure from the outside of the casing to the outside of the casing for the door width. In respect to this, how do you measure a barn door opening? You have to measure straight up to the right edge. The sliding barn door typically only has one panel, as it can slide in or out of place.