Free Tool
Free deck calculator
Enter your deck size and get the decking, joists, fasteners, and hangers you need, with board gap and joist spacing best practices built in. Free, no signup.
boards run this way
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Decking, framing, and the fasteners
Decking runs the length of the deck, so the width and your board size set how many rows you need. The calculator adds 10 percent for cuts and gives you the running feet to order.
A 1/8 inch gap between boards lets water drain and the wood breathe. Joists at 16 inches on center suit most lumber. Composite and PVC boards often want 12 inches so they do not feel bouncy or sag over time.
Fastening adds up fast. Two screws per board at every joist, or one hidden clip per intersection. Each joist gets a hanger at both ends. The calculator counts all of it, so you are not making a second hardware run halfway through.
Deck Calculator questions
How much decking do I need?
The board rows times the deck length, plus about 10 percent for cuts. The calculator gives the running feet so you can divide by your board length.
What joist spacing should I use?
16 inches on center for most wood. Drop to 12 for many composite and PVC boards so they do not sag or feel soft.
How many deck screws?
Two per board at each joist for face screws, or one hidden clip per intersection. The calculator counts them.
Is this really free?
Yes. No email, no signup, and nothing you type leaves your browser.
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Disclaimer: These free tools and templates are provided for general information and estimating purposes only. All results — including quantities, material and cost estimates, load, sizing, and span figures, scores, and any guidance or warnings — are rough approximations that may not fit your specific project, site conditions, local building codes, or current prices. They are not engineering, architectural, structural, legal, financial, or other professional advice, and are not a substitute for a licensed engineer, architect, contractor, or other qualified professional. Always confirm quantities, sizing, and structural, electrical, mechanical, and code requirements with a licensed professional and your local authority having jurisdiction before purchasing materials or performing any work. Werx makes no warranty as to accuracy and accepts no liability for any decision made using these tools. Use at your own risk. See our Terms of Service.