Decking Calculator
Estimate the boards, joists, beams, posts, and fasteners needed to build a deck from its dimensions, board size, board gap, and framing spacing, in imperial or metric units.
Input
Imperial enters the deck in feet and board/framing sizes in inches; metric uses metres and centimetres.
The direction the decking boards run (feet in imperial, metres in metric).
The direction the boards are laid side by side across (feet in imperial, metres in metric).
Face width of a single decking board (inches in imperial, centimetres in metric).
Length of one board as purchased (feet in imperial, metres in metric).
Expansion gap left between adjacent boards (inches in imperial, centimetres in metric).
Distance between joist centers along the deck's length (inches in imperial, centimetres in metric).
Distance between beam centers along the deck's width (feet in imperial, metres in metric).
Extra boards for cuts, breakage and future repairs (10% is typical).
Screws/nails per square foot in imperial, or per square metre in metric — check your fastening pattern.
Output
| Metric | Value |
|---|---|
| No data yet | |
One-line overview of deck area and total boards needed (with waste).
More ways to use this tool
REST API
curl -X POST https://api.iotools.cloud/v1/tool/decking-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"unitSystem": "imperial",
"deckLength": "12",
"deckWidth": "10",
"boardWidth": "5.5",
"boardLength": "12",
"boardGap": "0.125",
"joistSpacing": "16",
"beamSpacing": "8",
"wastePercent": "10",
"fastenerDensity": "3.5"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `decking-calculator` tool (Decking Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.
Embed widget
<iframe
src="https://iotools.cloud/embed/decking-calculator/"
width="100%" height="520" frameborder="0" scrolling="no" loading="lazy"
title="Decking Calculator — iotools.cloud"
sandbox="allow-scripts allow-forms allow-same-origin allow-downloads allow-popups allow-popups-to-escape-sandbox"
allow="clipboard-write"
style="width:100%;border:1px solid #e5e7eb;border-radius:12px;overflow:hidden"></iframe>
<script src="https://iotools.cloud/embed.js" async></script>Drop this into your own page — free, no key required, just a link back.
| Cost per API/MCP call | From 5 credits |
|---|---|
| Need more credits? | View pricing |
Also available with
Guides
Planning a deck build and need a materials list before you head to the lumberyard? This calculator turns your deck's dimensions, board size, and framing spacing into an estimate of the boards, joists, beams, posts, and fasteners you'll need — in imperial or metric units.
The frame it assumes
Most raised residential decks follow the same layout: decking boards run the deck's full length, laid side by side across its width with a small gap between them for drainage and expansion. Joists run perpendicular to the boards, spaced along the length, and each spans the deck's full width. Beams run parallel to the boards, spaced along the width, and each spans the deck's full length with a post supporting each end. That's the frame this calculator estimates against — a real design may add mid-span posts on long beams or extra blocking, which isn't modeled here.
Boards
- Rows across the width = deck width ÷ (board width + gap), rounded up.
- Boards per row = deck length ÷ board length, rounded up — how many boards you need end to end if a single board doesn't span the full length.
- Total boards = rows × boards per row, then increased by your waste percentage (10% is typical) for cuts, breakage, and future repairs.
Framing
- Joists: one every joist-spacing interval along the deck's length, plus one extra for the far end, each spanning the full width.
- Beams: one every beam-spacing interval along the deck's width, plus one extra, each spanning the full length — with a post at both ends.
- Fasteners: your chosen density (screws or nails per square foot/metre) multiplied by the deck's area.
How to use it
- Choose imperial or metric units.
- Enter the deck's length and width, and the board's width and length as sold.
- Set the gap between boards, joist spacing, and beam spacing — or leave the defaults (1/8" gap, 16" joists, 8ft beams for imperial).
- Adjust the waste percentage and fastener density if needed.
- Read off the board, joist, beam, post, and fastener counts.
Everything is computed locally in your browser — no upload, no sign-up.