A deck surface is rows of boards. The width of each board plus its gap sets how many rows fit across.
Deck board calculator
Boards run along the length. Enter the board width you are buying and the gap.
Enter your numbers to see the result.
How it works
Rows = deck width / (board width + gap), rounded up. Each row needs deck length / board length boards, rounded up. Joists = deck length / spacing + 1.
A 16 x 12 ft deck with 5-1/2 in boards and 1/4 in gaps needs 26 rows of one 16 ft board, or 29 boards with 10% extra.
Gaps and spacing
Wood and composite boards have different gap and joist-spacing rules, and some composite boards need closer joists when laid on a diagonal. Use the numbers from the board maker’s installation guide.
Board length
Matching board length to deck length avoids butt joints. If the deck is longer than your boards, stagger the joints and land each one on a joist.
Frequently asked questions
How many deck boards for a 12 x 12 deck?
With 5-1/2 in boards and 1/4 in gaps, 26 rows of a 12 ft board, about 29 with 10% extra.
How wide is a 5/4 x 6 deck board?
Usually about 5-1/2 in. Check the actual width of the boards you buy.
How far apart are deck joists?
Often 16 in on center, but the board maker and your plans decide.