Decking board calculator
How many boards, and how many linear feet. Counting the gap between them, because that gap is coverage.
Decking
| Item | Qty | Unit |
|---|---|---|
| 5/4x6 decking, 16 ft lengths 26 rows across 12 ft of width. Each board covers 5.75 in (5.50 in face + 0.25 in gap), so 12 ft of width needs 26 rows. 26 rows x 16 ft = 416 linear ft, plus 10% cutting waste for a straight layout = 458 linear ft, bought as 16 ft boards. | 29 | each |
How this calculator works
Why the gap changes the answer
Deck boards are spaced apart so water drains and the boards can move. A 5.5 in board with a 1/4 in gap occupies 5.75 in of deck. Over a 12 ft width that is the difference between 26 rows and 27 — one full row of boards you would otherwise buy and not need.
Board length decides your seams
If your deck is longer than the boards you can buy, every row needs a butt seam. Seams must land on a joist, and most builders double the joist beneath a seam line. Picking a board length that divides evenly into your deck length avoids both the waste and the extra framing.
What waste really covers
Waste is not a safety margin, it is the offcuts your layout creates. Straight runs produce little. Diagonal layouts cut both ends of every board at an angle. A picture frame adds mitres at every corner of the border. Buying a flat 10% for a diagonal deck leaves you short.
What we will not guess
Joist and beam span limits are structural-safety data. Until our span tables are verified line by line against the published AWC DCA6 tables, this site withholds them and says so, rather than printing a number that looks authoritative. Footing depth must reach below your local frost line, which varies from nothing in the far south to over eight feet in the far north. Confirm both with your local building department — see our methodology.
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