Deck Board Calculator
How many deck boards a deck needs, allowing for the gap between them, plus the screws to fix them down.
Enter the deck size, the board you are buying and the gap you want between boards. This works out the board count, the screws, and the linear feet to order.
Your details
The direction the boards RUN along.
The direction the boards are laid ACROSS.
A nominal 6-inch board is usually 5.5 in actual.
For drainage and movement. 1/8 to 1/4 in is typical.
On centre. 16 in is the most common.
Result
Full-length boards, waste included.
- Boards to cover the deckBefore any allowance for cuts and rejects.
- 26
- Linear feet to orderBoards multiplied by their length - how timber is often priced.
- 448
- Screws neededTwo per board at every joist crossing.
- 728
- Deck areaSquare feet of deck surface.
- 192
About this tool
How Many Deck Boards Do I Need?The count comes from the width you're spanning, not the area — and the gap between boards changes it. The arithmetic, and the mistakes it prevents.
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Deck Materials Take-OffMeasure the deck, total the boards and screws, and take one list to the yard. Same figures this calculator uses.
Free, no email required — print it or save it as a PDF.
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Deck Board Calculator infographicThe key numbers as one image — free to save, share, or embed on your own site with credit.
How this is calculated
The board count comes from the width the deck has to span, not from its area. Boards run in one direction, so what matters is how many board-widths fit across the other one. Each board effectively occupies its own width plus one gap, because every board takes a gap alongside it. Board width is entered in inches and divided by 12 to bring it into feet. A 5.5 inch board with a 0.25 inch gap occupies 5.75 inches of deck for every board laid, so you need slightly FEWER boards than the deck width alone suggests - the gap is deck you do not have to fill with timber. Boards are then rounded up, and a waste allowance is added on top for cuts, splits and the boards you reject at the yard. Screws are two per board at every joist crossing. Joist spacing is an input because it varies; 16 inches on centre is the most common. This assumes a rectangular deck with boards running in one direction and no picture-frame border, no diagonal, and no mitred corners - all of which use noticeably more.
Common questions
- Why does the gap change the board count?
- Because every board takes up its own width plus the gap beside it. A quarter-inch gap on a 5.5 inch board means each one occupies 5.75 inches of deck rather than 5.5. Across a 12 foot deck that is 26 boards instead of 27 - the gap is deck you do not have to fill with timber.
- What gap should I leave?
- An eighth to a quarter of an inch is typical, for drainage and for the board moving with the weather. Pressure-treated timber that is still wet when you lay it will shrink, so it is usually laid tighter; composite and dry timber are laid at the full gap.
- Which measurement is the length?
- The length is the direction the boards run ALONG. The width is the direction you are laying them ACROSS - that is the one the board count comes from. Swapping them gives a very different answer.
- Does this cover a picture-frame border or diagonal boards?
- No. A border adds boards and a lot of mitred cuts; laying on the diagonal typically wants around 15 percent more material because every board meets the edge at an angle. Raise the waste allowance well above 10 for either.
- Are the screws right for hidden fasteners?
- No. The screw figure is two face screws per joist crossing. Hidden fastener systems are priced per square foot or per board and have their own coverage figures on the box.
Take it further with AI
Copy this into ChatGPT or Claude with your own numbers filled in. It hands over the figures this calculator worked out, so the answer is built on real arithmetic instead of a guess.
I used the Deck Board Calculator at https://www.bfcbrilliance.com/tools/deck-board-calculator.
What I entered:
- Deck length (ft): ___
- Deck width (ft): ___
- Board width (in): ___
- Gap between boards (in): ___
- Joist spacing (in): ___
- Waste allowance (%): ___
What it calculated:
- Boards to buy: ___
- Boards to cover the deck: ___
- Linear feet to order: ___
- Screws needed: ___
- Deck area: ___
Use those figures as given — they are already worked out, so please don't recalculate or estimate your own. Help me turn them into a plan: what to buy or do, in what order, roughly what it should cost, and the mistakes people most often make with this job.
Where the job touches structure, gas, or electrics, tell me to check local building code and whether a permit or a licensed trade is required.Last updated
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Part of a bigger job
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Walks through all 5 decking & fencing tools in order.