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Deck board calculator
Put your deck size, board width and gap in: a 16 ft by 12 ft deck with 5.5 in boards and a 0.25 in gap needs 26 boards — 416 linear feet.
★ CONSTRUCTION · DECK · BOARDS
Deck Board Calculator: 26 Boards for a 16×12 ft Deck
On the defaults — a 16 ft by 12 ft deck, 5.5 in boards, a 0.25 in gap — you need 26 boards, or 416 linear feet. This is the deck-board tool: measure the deck once, and order the boards once, with the last board trimmed rather than a board short.
What does deck boards needed 26 mean?
It means 26 boards, each 16 ft long, laid side by side, cover a 12 ft wide deck when each board takes 5.75 in of width — its own 5.5 in plus a 0.25 in gap. The count comes from the width, not the length: 144 in of deck width divided by 5.75 in per board is 25.04 boards, and you cannot buy 0.04 of a board, so it rounds up to 26. The last board gets trimmed to fit the remaining sliver, which is why the linear feet — 26 times 16 ft, or 416 ft — is the number the timber yard actually cuts.
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Width in inches | deck width × 12 | 144 in — 12 × 12. |
| Width per board | board width + gap | 5.75 in — 5.5 + 0.25. |
| Boards across | width in inches ÷ width per board, rounded up | 26 boards — 144 ÷ 5.75 = 25.04. |
| Linear feet | boards × deck length | 416 linear feet — 26 × 16. |
Three things to check before you trust the number
First, check whether your board width is the face width or the nominal width: a board sold as 6 in is usually 5.5 in across the face, and using 6 in here undercounts by a board on a deck this size. Second, decide the gap before you count: a 0.5 in gap instead of 0.25 in drops this deck to 24 boards, but a gap wider than the board maker recommends looks gappy and lets small things through. Third, remember the count is boards across only — framing, joists, posts and rails are a separate list, and this calculator does not size them.
Worked example
16 ft long, 12 ft wide, 5.5 in boards, 0.25 in gap. Width in inches: 12 × 12 = 144 in. Width per board: 5.5 + 0.25 = 5.75 in. Boards: 144 ÷ 5.75 = 25.04, round up to 26. Linear feet: 26 × 16 = 416 ft. In practice that means ordering 26 boards of 16 ft, and expecting the last one to be ripped down to a narrow strip — keep that offcut, since it is the spare piece for a damaged board later. If the same deck used 7.25 in boards instead, the count would fall to 20 boards and 320 linear feet, but the deck area covered would be identical.
Every branch, checked
With a 20 ft long deck instead of 16 ft, the board count stays 26 — length never changes how many boards fit across — but the linear feet rise to 520 ft, since every board is four feet longer. With a 14 ft wide deck, the count rises to 30 boards and 480 linear feet. With 7.25 in boards, the count falls to 20 boards and 320 linear feet. With a 0.5 in gap, the count falls to 24 boards and 384 linear feet. Width, board width and gap move the count; length moves only the footage.
The reverses, worked backwards
The width behind 26 boards is 12 ft: at 10 ft the need is 21 boards (336 linear feet); at 14 ft it is 30 boards (480 linear feet). The board width behind 26 boards is 5.5 in: at 4.5 in the need is 31 boards (496 linear feet); at 6.5 in it is 22 boards (352 linear feet). The gap behind 26 boards is 0.25 in: with no gap the need is 27 boards (432 linear feet); at a 0.5 in gap it is 24 boards (384 linear feet). Each reverse moves one input and holds the rest, so the step is exactly one dimension or one gap change.
What the defaults assume
The defaults assume a 16 ft by 12 ft rectangular deck, boards running the 16 ft length, 5.5 in face width, and a 0.25 in gap. They do not assume a picture-frame border, diagonal boards, stair treads, or waste for bad boards — diagonal laying adds roughly 10% to the footage, and a couple of spare boards cover the one that arrives split.
Who uses this
- A homeowner pricing a new deck: the 26-board count and 416 linear feet turn a sketch into a timber-yard list.
- A DIY builder mid-project: the gap branch shows whether widening the gap saves a board or just looks wrong.
- A contractor quoting a job: boards across, then footage, then price — the quote follows the same three steps.
- A renovator re-boarding an old frame: the width and board width, measured off the existing frame, give the new board count directly.
Accuracy & limitations
The arithmetic is exact for the inputs entered; the judgement is the board width and the gap. Real boards vary slightly in width, a deck is rarely a perfect rectangle, and the last board is trimmed rather than counted whole — so treat 26 boards as the planning count and buy one or two spares for splits and miscuts. If the boards run diagonally or a border frame is planned, add about 10% to the linear feet before ordering.
Cite this calculator
Bright Side Kit, “Deck Board Calculator: 26 Boards for a 16×12 ft Deck”, https://brightoolbox.com/deck-board-calculator/, accessed 2 November 2026. Students and researchers: cite the calculator name, the page URL and the date you used it, and quote the defaults (16 ft × 12 ft deck, 5.5 in boards, 0.25 in gap) so the 26-board result can be checked.
Frequently asked questions
How many deck boards do I need for a 16×12 deck?
26 boards of 16 ft — 416 linear feet. The 12 ft width is 144 in, each board takes 5.75 in including its gap, and 144 ÷ 5.75 = 25.04, rounded up to 26.
Does deck length change the board count?
No — length changes only the linear feet. A 20 ft long deck still needs 26 boards across, but 520 linear feet instead of 416, since every board is longer.
What gap should I leave between deck boards?
About 0.25 in for most composite and timber boards: enough for drainage and swelling, tight enough to look finished. Check the board maker’s guide — some boards specify a different gap, and the gap changes the count.
Should I buy extra boards?
Yes, one or two spares. Boards arrive split or get miscut, and a spare from the same batch matches the colour. Diagonal boards need about 10% extra footage on top of the count here.
What is the difference between nominal and face width?
A board sold as 6 in is usually 5.5 in across the face after planing. Enter the face width — the width you can actually stand on — or the count comes out low by a board or more.
How do I price the boards once I know the count?
Multiply linear feet by the per-foot price, or boards by the per-board price, and add framing separately. The deck cost calculator does that sum for the same deck.