Deck Calculator Widget
Give deck builders and DIYers a material take-off. From the deck size, board width and gap, board length and joist spacing, the widget counts the decking boards, the joists and the screws, so a lumber-yard order or a quote can start from real numbers.
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Under the widget on your page: Powered by A2Z Tools
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<iframe src="https://a2z.tools/embed/w/deck-calculator" title="Deck Calculator by A2Z Tools" width="100%" height="860" style="border:0;width:100%" loading="lazy" allow="clipboard-write"></iframe>
A plain iframe. Works everywhere, including site builders that strip scripts. Adjust height if your content needs more room.
<div data-a2z-widget="deck-calculator" data-height="860"></div> <script async src="https://a2z.tools/embed.js"></script>
Adds a small script (what it does) that sizes the widget to fit its content, loads it lazily and keeps it isolated from your page's CSS.
Works with
How it works
Boards are assumed to run along the deck length and sit on joists that run across it. The number of board rows is the deck width divided by one board plus one gap, rounded up - a 12 ft wide deck with 5-1/2 in boards and 3/16 in gaps needs 25.3, so 26 rows, the last one ripped to width. Rows times deck length gives the linear footage laid; the waste allowance is added and the total divided by the board length you can buy, rounded up. Joists are the deck length divided by the spacing, rounded up, plus one so both ends are carried: 16 ft at 16 in centres is 13 joists. Screws are two per board at every joist it crosses, rows x joists x 2. Imperial mode uses feet and inches with 12, 16 or 24 in centres; metric uses metres and millimetres with 300, 400 or 600 mm.
Calculation method
- Rows = ceil(deck width / (board width + gap))
- Linear decking = rows x deck length x (1 + waste / 100); boards = ceil(linear / board length)
- Joists = ceil(deck length / joist spacing) + 1, each the deck width long
- Screws = rows x joists x 2 (two per board per joist)
Worked examples
16 x 12 ft timber deck
Inputs: Boards 5.5 in with 3/16 in gaps, 16 ft long; joists at 16 in; 10% waste
Result: 29 boards, 13 joists, about 676 screws
144 / 5.6875 = 25.3 -> 26 rows; 26 x 16 = 416 ft; x 1.10 = 457.6 ft / 16 = 28.6 -> 29 boards; 192 / 16 + 1 = 13 joists; 26 x 13 x 2 = 676.
4.8 x 3.6 m deck in metric
Inputs: 140 mm boards, 5 mm gaps, 4.8 m lengths; joists at 400 mm; 10% waste
Result: 28 boards, 13 joists, about 650 screws
3,600 / 145 = 24.8 -> 25 rows; 25 x 4.8 = 120 m; x 1.10 = 132 m / 4.8 = 27.5 -> 28.
Material quantities for planning only - not a structural design. Follow your local code or an engineer for spans and footings.
Limitations
- No structural design: joist size, span, beams, posts, footings and ledger fixing are not checked.
- Rectangular decks only; stairs, railings, fascia and picture-frame borders are extra.
- Board count assumes offcuts are not reused across rows; joining offcuts on joists can lower it.
Where publishers use it
- Lumber yards and composite-decking dealers listing a board product
- Backyard DIY blogs with a step-by-step deck build
- Deck builders' sites that collect a project size before a site visit
- Outdoor-living magazines comparing composite and timber budgets
- Holiday-home and cabin renovation guides
Questions
What gap should I leave between deck boards?
Timber decking is commonly gapped about 1/8-1/4 in (3-6 mm) to drain and allow for swelling; composite makers specify their own gaps, often with hidden clips that set it. Use the manufacturer's figure.
Which joist spacing should I choose?
16 in (400 mm) centres suit most timber and composite boards laid square to the joists; 12 in is often required for diagonal decking or thinner composite boards, and 24 in only for boards rated for it. Spacing for decking is a product rule - check the board's installation guide.
Why two screws per joist?
Each board is face-fixed with two screws at every joist it crosses, one near each edge. A 16 x 12 ft deck with 26 rows on 13 joists needs 676 screws; buy a box that also covers end joints and a few spares.
Does the widget size my joists or beams?
No. Joist depth, span, beams, posts and footings depend on loads, timber grade and local code - the widget only counts quantities. Use a span table or an engineer for the structure.
How much waste should I allow on decking?
About 5-10% for straight runs where board lengths suit the deck, and 15% for diagonal layouts or when end joints must fall on joists.
Should deck boards be hidden-fastened or face-screwed?
Composite and PVC boards are often grooved for hidden clips, one per joist crossing, which leave the surface clean; timber is usually face-screwed with stainless or coated deck screws. The screw count here is for face fixing - count clips instead for grooved boards.
How do I frame a picture-frame border?
A border board runs around the perimeter with mitred corners, and the field boards butt into it. It needs extra blocking under the border and adds roughly the deck's perimeter in linear footage; add those boards separately.
Cite or recommend this tool
If you reference this tool in an article, course or documentation, these formats are ready to copy. They are optional - nothing is added to your site unless you paste it.
A2Z Tools Deck Calculator https://a2z.tools/embed/deck-calculator
<a href="https://a2z.tools/embed/deck-calculator">A2Z Tools Deck Calculator</a>
[A2Z Tools Deck Calculator](https://a2z.tools/embed/deck-calculator)
Deck Calculator by A2Z Tools - https://a2z.tools/embed/deck-calculator
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