How to calculate deck boards
The number of rows is the deck width divided by the board width plus the gap. Each row needs enough boards to cover the deck length. Choosing a board length that divides the deck evenly (for example 16 ft boards on a 16 ft deck) saves a lot of waste.
Joists and screws
Joists usually sit 16 in (40 cm) apart, closer (12 in / 30 cm) for composite boards or diagonal decking. Every board gets two screws at every joist it crosses.
Gaps
Leave about 3/16 in (5 mm) between boards for drainage and movement. Wet pressure-treated boards shrink as they dry, so they can be laid tight.