Corner bead protects and straightens outside (convex) drywall corners — the edges that stick out into a room, like the corner of a hallway or the edge of a doorway opening. Unlike inside corners, which are simply taped, outside corners need a rigid metal or vinyl bead fastened over the joint before mudding, so the quantity needed is driven entirely by how many outside corners a room has and how tall each one is.

This calculator multiplies your outside corner count by the corner height to get total linear footage, adds a waste allowance for trim cuts and mistakes, and then divides by the stick length your supplier sells to get a shopping-list number of full sticks, rounding up since bead is not typically field-spliced mid-run on a single corner.