Do I need blocking and where?

Provide blocking at midspan for longer joists, at cantilevers, and at transitions as needed. See the Blocking Spacing tool and follow code.

🧮Free & instant

Deck Joist Spacing & Span — Fast, Simple, Planning Estimates

Q: What’s the proper deck joist spacing?

Common spacings are 12, 16, or 24 inches on center. Composite decking often needs 16 in. o.c. or 12 in. when boards run diagonal. Use the Deck Joist Spacing Calculator and verify with local code and manufacturer instructions.

Q: How far can a deck joist span?

It depends on joist size, species/grade, spacing, and design loads. Use the Deck Joist Span Calculator as a planning estimate and confirm with official span tables and your inspector.

Start with the Deck Joist Spacing Calculator or try the quick estimator below. Works for wood or composite decking. Always confirm with your local code/inspector.

Joist Size

Clear Span (feet)

Decking Type

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Deck Joist Spacing Calculator Deck Joist Span Calculator Deck Beam Size Calculator Cantilever Calculator Blocking Spacing

Planning tool only. Results are estimates. Follow the International Residential Code (IRC) and manufacturer instructions; consult a licensed pro/inspector.

What you can calculate

📏 Deck joist spacing calculator — 12″/16″/24″ o.c. recommendations
📐 Deck joist span calculator — estimated maximum spans per size
🪵 Deck beam size calculator — quick suggestions for common loads
↔️ Cantilever limits — simple ratios (joist backspan required)
🧱 Blocking spacing — rows and placement guidance

Deck Joist Spacing Chart

Compare 12″ vs 16″ vs 24″ on-center and how composite decking affects spacing.

Open chart

Deck Joist Span Chart

See typical spans for 2×6, 2×8, 2×10, 2×12 under common loads.

View spans

Composite Decking

Most brands want ≤16″ o.c. (often 12″ on diagonal). Check your manufacturer.

Composite notes

FAQ

What’s the proper deck joist spacing?

Common spacings are 12″, 16″, or 24″ on-center. Composite decking often requires 16″ o.c. (or 12″ when boards are diagonal). Our Deck Joist Spacing Calculator suggests an option based on span and joist size.

How far can a deck joist span?

It depends on lumber size, species/grade, spacing, and loads. See the Deck Joist Span Calculator and verify with official span tables and your inspector.

Do I need blocking?

Typically one row at midspan for longer joists (and at cantilevers), plus at beam/frame transitions. Use the Blocking Spacing tool for a quick plan and follow code.