How to use the deck board calculator
- Enter the Deck length (along the boards) and Deck width (across the boards).
- Choose a Board width (5.5 in or 3.5 in) and enter the Gap between boards.
- Pick the Board length you plan to buy.
- Set the Joist spacing (16 in is standard) and the Extra for cuts.
- Optionally enter a price per board to estimate cost.
How it works
The calculator works out how many rows of boards span the deck width, then the total linear feet of decking. It adds your extra for cuts and divides by the board length you buy.
Joists are counted along the deck length at your spacing, and screws assume two per board at every joist. This covers decking boards only; framing, footings and railings need a design that meets your local building code.
Rows = deck width (in) ÷ (board width + gap), rounded up
Boards = rows × deck length × (1 + extra %) ÷ board length, rounded up
Joists = deck length (in) ÷ joist spacing, rounded down, + 1
Screws = rows × joists × 2
Worked example
With the default inputs, a 16 × 12 ft deck with 5.5 in boards and ⅛ in gaps needs 144 ÷ 5.625 = 25.6, so 26 rows. That is 416 linear feet.
With 10% extra, 457.6 ft ÷ 16 ft boards = 28.6, so buy 29 boards. Joists at 16 in on center number about 13, and 26 rows × 13 joists × 2 = 676 screws.
Tips before you buy
- Choose a board length that matches the deck length, or plan to stagger butt joints over joists.
- Composite boards often need joists 12 in on center; check the manufacturer’s span table.
- Follow the board maker’s gap guidance, since some boards shrink or expand after installation.
- Decks usually need a permit, and ledger, footing and railing details must meet local building code.
- Call 811 before digging footing holes.
Frequently asked questions
How many deck boards do I need for a 16×12 deck?
With 5.5 in boards, ⅛ in gaps and 10% extra, about 29 boards 16 ft long, running the 16 ft direction.
How far apart should deck boards be?
About ⅛ in is common for many wood and composite boards. Check the manufacturer’s instructions for your board.
How many screws do I need for a deck?
Plan on two screws per board at every joist. The default 16 × 12 ft deck has 26 rows and about 13 joists, so 676 screws.
What joist spacing should I use?
16 in on center is standard for most wood decking. Composite boards and diagonal layouts often need 12 in. Follow your board’s span rating and local code.
Does this calculator include framing lumber?
No. It counts decking boards and screws and gives an approximate joist count. Beams, posts, footings and railings need a design that meets local code.
Results are estimates based on the measurements you enter and typical material properties. Products vary, so check quantities with your supplier and follow product labels and your local building codes. Read the full disclaimer. Last reviewed October 9, 2026.