Deck Boards
Rows across width × board run; 8% waste.
About this calculator
This calculator figures out how many rows of deck boards a deck needs and the total linear feet to purchase, including an 8% waste allowance for cuts and defects. Width (the dimension perpendicular to the board run) and Board width both drive Rows, but in opposite directions: a wider deck needs proportionally more rows, while wider individual boards mean fewer rows are needed to cover the same width, since each row's footprint is the board's face width plus the gap between boards. Board run (the direction the boards actually span) doesn't affect Rows at all -- it only scales the final linear-feet total once the row count is already fixed, since more rows times a longer run both mean more total board length to buy.
Gap, the spacing left between boards for drainage and expansion, is real and does reduce the number of rows needed as it grows, but its effect is small next to Board width or Width, since a typical 1/8-inch gap is a tiny fraction of a board's face width. The 8% multiplier applied at the end accounts for waste from cutting boards to length and culling defective sections, a standard estimating allowance for deck board takeoffs.
Inputs
Results
Rows
30
How to Use This Calculator
- Enter the board run length in feet (the direction boards span, typically the long dimension).
- Enter the deck width in feet (the direction you count rows of boards).
- Enter the face width of each board in inches — a standard 5/4×6 deck board has a 5.5 inch face.
- Enter the gap between boards in inches — 1/8 inch (0.125) is a common spacing.
- Read the number of board rows needed and total linear feet to purchase including 8% waste.
How the result changes with Width (ft)
| Width (ft) | Rows |
|---|---|
| 7 | 15 |
| 11 | 24 |
| 21 | 45 |
| 35 | 75 |
What each input means
- Board run (ft)
- Length each board spans (the direction boards run). Typically the longer deck dimension.
- Width (ft)
- Width of the deck perpendicular to board direction. Determines how many rows are needed.
- Board width (in)
- Actual face width of each deck board in inches. A standard 5/4x6 board has a 5.5-inch face.
- Gap (in)
- Spacing between boards for drainage and expansion. 1/8 inch (0.125) is typical.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersBoard run (ft) = 18, Width (ft) = 14, Board width (in) = 5.5, Gap (in) = 0.125 = 4 input(s) provided
- Calculate RowsRows30 = 30
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why do wider boards mean fewer rows, while a wider deck means more rows?
Rows is the deck's Width converted to inches and divided by each board's total footprint (Board width plus Gap), so a wider deck needs more of that footprint to fill, increasing Rows, while a wider individual board covers more of that same width per row, decreasing the number of rows needed.
Does the length of the deck affect how many rows I need?
No -- Board run (the deck's length in the direction boards span) only affects the final Linear Feet total once Rows is already calculated from Width and Board width; a longer deck needs more linear feet of board per row, but it doesn't change how many rows there are.
How much does the 8% waste factor add to my linear feet total?
It multiplies the raw calculated linear feet (Rows times Board run) by 1.08, adding roughly 8% extra material to account for miscuts, defective sections, and trim waste -- a standard estimating allowance so you don't come up short partway through installing the deck boards.
Does changing the gap between boards make a big difference in materials?
It has a real but small effect -- increasing Gap slightly increases each row's footprint and can reduce the number of rows needed, but because a typical 1/8-inch gap is tiny next to a board's 5.5-inch face width, its effect on Rows is much smaller than changing Width or Board width.
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