Deck Board Calculator
How many deck boards and rows you need for a deck of any size.
Input sheet
DIY at your own risk. Calcora's calculators and guides are general estimates and information only — not professional, engineering, legal, or safety advice. Always verify local building codes and permit requirements, and hire a licensed pro for electrical, gas, plumbing, structural, or any work you're not fully comfortable doing yourself.
A deck's board count comes down to how many rows fit across its width once you account for the gap between boards — and that gap, multiplied across dozens of rows, changes the total. This calculator does the row math so you order the right number.
How it works
Deck width in inches divided by board width plus gap gives the number of rows; one board per row runs the deck length.
The calculator converts deck width to inches and divides by the board width plus the gap to get the number of rows. One board per row runs the full deck length, so the board count equals the row count, and total linear feet is rows times length.
The gap between boards isn't waste — it lets the deck drain and lets boards expand. A 1/8-inch gap is typical for kiln-dried lumber; wet pressure-treated boards are often installed tight because they shrink as they dry.
Rows = (deck width × 12) ÷ (board width + gap), rounded up; boards = rows; linear feet = rows × deck length.
Worked examples
A 16 ft × 12 ft deck with 5.5-inch boards and a 1/8-inch gap. → 26 boards (16 ft each), about 416 linear feet.
Width 12 ft = 144 in ÷ (5.5 + 0.125) = 144 ÷ 5.625 ≈ 25.6, rounded up to 26 rows. 26 boards × 16 ft = 416 linear ft.
A 10 ft × 10 ft deck with 5.5-inch boards and a 1/8-inch gap. → 22 boards (10 ft each), about 220 linear feet.
Width 10 ft = 120 in ÷ 5.625 ≈ 21.3, rounded up to 22 rows × 10 ft = 220 linear ft.
Tips & gotchas
- Add about 10% for cuts, waste, and any diagonal or picture-frame border pattern that increases the board count.
- Boards run the long dimension here — if you run them the other way, swap your length and width inputs.
- Buy a few extra boards from the same batch; color and grain vary between deliveries and a mid-deck replacement will stand out.
- Don't forget joists, ledger, fasteners, and any railing — the board count is only the surface decking.
FAQ
What gap should I leave between deck boards?
About 1/8 inch for dry boards. Wet pressure-treated lumber can go in nearly tight since it shrinks as it dries — leaving a gap then can result in gaps too wide once the wood cures.
Should deck boards run the length or width of the deck?
Either works structurally as long as joists run perpendicular. Boards are usually run so the seams fall over joists with the fewest cuts; the calculator assumes boards span the length you enter.
Does the calculator include joists and framing?
No — it counts only the surface decking boards. Framing lumber, fasteners, and railing are separate and depend on your joist spacing and design.
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