Deck Board and Joist Calculator

Count the deck boards, joists and screws for a rectangular deck from its size, board width, gap and joist spacing, and estimate the cost.

Deck Width (Ft.)

Along the house. Boards run this way.

Deck Depth (Ft.)

Out from the house. Joists run this way.

Decking

Board Width

Width (In.)

Gap (In.)

Board Length (Ft.)

Framing

Joist Spacing

Screws per Board per Joist

Extra Decking (%)

Cost

Per Deck Board

Per Joist

Per 100 Screws

Deck Name

Fractions work too: try 3/16.

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Deck Boards

Deck area
Rows of boards
Decking
Joists
Rim and ledger
Screws
Cost: Add prices to estimate

Deck List

Decks you add are saved in this browser.

Deck	Size	Boards	Joists	Screws	Cost	Remove

How to Figure Deck Boards and Joists

Deck boards usually run parallel to the house, across the joists. Each row of boards covers one board width plus one gap, so divide the deck's depth by that to get the number of rows. If the deck is wider than your boards are long, each row takes more than one board, with the joints landing on joists.

Rows = ⌈depth (in) ÷ (board width + gap)⌉ Boards per row = ⌈deck width ÷ board length⌉

Joists = ⌊deck width (in) ÷ spacing⌋ + 1 Screws = rows × joists × screws per crossing

Worked Example

Rows of Decking per Foot of Depth

Board	Gap	Coverage per Row	Rows per 10′

Tips for Decking

Check the decking maker's instructions for gap and joist spacing: many composite boards call for 16″ spacing or closer, and 12″ when boards run on a diagonal. Wet pressure-treated boards shrink as they dry, so they're often laid tight and allowed to open up. Stagger butt joints across different joists. Joist size and span, beams, posts and ledger attachment should follow your local code, such as the American Wood Council's DCA 6 deck guide.