Door slab and track size vs. the opening — swing, barn, bypass, and pocket compared

What this diagram shows

Four small elevations comparing how a door’s slab or track relates to the finished opening, because the slab width is not the same as the opening width for sliding doors. A pre-hung swing door fills its opening: the rough opening equals the door plus 2 inches. A barn door must be wider than the opening — about 4 to 6 inches wider so it overlaps and covers the gap on each side — and its wall-mounted track has to be at least twice the slab width so the door can slide fully clear. A bypass closet uses two doors on parallel tracks, each about half the opening plus a half inch of overlap where they meet. A pocket door slides into a hollow pocket built inside the wall, so its rough opening is roughly twice the door width plus 1 inch to hold both the doorway and the pocket. This is why the calculator asks for the opening as well as the door.