Deck Board Count Calculator
Count the deck boards for a rectangular deck from its size, board width and gap — with linear feet and the number of rows.
How it works
rows = ⌈width in inches ÷ (board width + gap)⌉ · linear feet = rows × deck length · boards = ⌈linear feet × (1 + waste%) ÷ board length⌉
Each row of decking covers the board’s face width plus one gap, so the number of rows is the deck’s width divided by that combined figure, rounded up. Multiplying rows by the deck length gives the total linear feet of board, which you then convert to purchased boards of a standard length. A gap of 1/8 to 1/4 in lets the boards drain and expand; wider gaps mean slightly fewer rows.
Worked example
A 16 × 12 ft deck with 5.5 in boards and a 3/16 in gap: each row spans 5.6875 in, so 144 ÷ 5.6875 = 25.3, rounded to 26 rows. That is 26 × 16 = 416 linear ft; with 10% waste, 458 ft ÷ 16 ft boards = 29 boards.
Frequently asked questions
Which way should deck boards run?
Boards usually run the long direction of the deck or diagonally for looks, and always perpendicular to the joists. This calculator assumes boards run along the length you entered, so the rows stack across the width.
What gap should I leave between boards?
Leave about 1/8 to 1/4 in for drainage and airflow. Pressure-treated boards that are still wet shrink as they dry, so gap them tighter (around 1/8 in); dry or composite boards get the fuller gap.
Why add waste for decking?
End cuts, board defects and the offcuts from fitting around posts and stairs all add up. Ten percent is typical for a plain rectangle; a deck with angles, picture-frame borders or diagonal boards can waste 15% or more.
Related calculators
Estimates only — add for waste and confirm against local building codes and supplier specs.