How many deck boards do I need?
Count the rows (deck width ÷ board width plus gap), multiply by the boards per row (deck length ÷ board length, rounded up), then add waste.
A 16 × 12 ft deck with 5½ inch boards and 1/8 inch gaps: 144 ÷ 5.625 = 26 rows. With 16 ft boards that's one board per row, 29 boards with 10% waste, and 26 × 13 joists × 2 = 676 screws.
What the deck guide says
From the American Wood Council's Prescriptive Residential Wood Deck Construction Guide (DCA 6):
- Fasteners: 2 #8 screws or 2 8d threaded nails at every joist.
- Gap: space boards approximately 1/8 inch apart.
- Support: each piece of decking must bear on at least 3 joists.
- Angle: boards may run perpendicular to the joists or at up to 45°.
Plan the butt joints
If the deck is longer than your boards, joints must land on a joist. Stagger them from row to row, and pick a board length that divides the deck evenly to cut waste.
Structure is a permit job
This calculator counts decking only. Joist size, beams, footings and ledger attachment follow DCA 6 or your local code, and most decks need a permit.
Frequently asked questions
How many deck boards do I need?
Divide the deck width (across the boards) by the board width plus the gap to get the number of rows, then multiply by how many boards each row takes. Add about 10% for cuts and defects.
How far apart should deck boards be?
The American Wood Council's DCA 6 guide says to space decking boards approximately 1/8 inch apart. Composite makers publish their own gaps, so follow the brand's instructions.
How many screws per deck board?
DCA 6 calls for 2 #8 screws or 2 8d threaded nails at every joist. A 16 ft board over joists 16 inches apart crosses 13 joists: 26 screws.
What joist spacing do deck boards need?
DCA 6 notes that products sold as decking are usually rated for 16 or 24 inch spans. 16 inches on center is the most common joist spacing for residential decks.
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