When determining the size of a master bedroom walk-in closet, match it to the room's dimensions. For smaller bedrooms, aim for 12-14 inches wide, 5-8 feet in length, and 7-8 feet in height. Medium-sized rooms fit closets 14-16 inches wide, 8-10 feet in length, and 8-9 feet in height. Larger bedrooms suit closets 16-18 inches wide, 10-12 feet in length, and 9-10 feet in height.