From deck size to board count
Decking is estimated by how much area each board covers. A board's coverage is its width plus the installation gap, multiplied by its length, so wider boards and bigger gaps cover more area each. Dividing the deck area by that coverage gives the raw board count, and a waste allowance covers cuts and the occasional defective board.
Planning the deck layout
Plan board runs to minimize cuts and avoid short end pieces, and stagger end joints over joists for strength and appearance. Decorative choices such as diagonal boards or a picture-frame border look great but add waste and labor. Always size joists, beams and fasteners to code as a separate step from the decking itself.