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Deck Joist Calculator

Result
—joists
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CalcBuild › Deck Joist Calculator

How to Calculate Deck Joist

Use this free deck joist calculator to get instant, accurate results for your construction project. Simply enter your measurements above and the calculator will automatically compute the result using industry-standard formulas.

Pro Tip: Always add 10-15% extra material to account for waste, cuts, and job-site conditions. This is standard practice recommended by experienced contractors.

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▸ Ceiling Joist▸ Composite Deck▸ Composite Deck Cost▸ Concrete Pier Deck▸ Deck Board▸ Deck Board Spacing

💡 Pro Tips — Deck Joist

❓ Frequently Asked Questions

+What joist spacing for composite?
12" on center for composite decking (it flexes more than wood). 16" OC is fine for wood decking.
+How deep do footings need to be?
Below your local frost line. 42" in cold climates (MN, WI), 24" moderate, 12" in the South. Check local code.
+Do I need a permit?
Yes for most decks over 30" above grade. Attached decks often require engineering for the ledger board connection.
+How long does composite last?
25-30+ years with zero maintenance. Most brands offer 25-year fade and stain warranties.