Free layout planner with visual diagram. Calculate post positions, beam sizes, and footing requirements per IRC 2021. Shows exactly where to place every post for your deck project.
💡
Standard deck posts: 6-8 feet apart (4×4 max 6ft, 6×6 max 8ft)
Railing posts: Max 6 feet for code compliance. Exact spacing depends on beam size, joist span, and wood species.
✓Visual Layout Diagram
✓IRC 2021 Compliant
✓6 Wood Species
📐 Deck Dimensions & Settings
ft
ft
💡 Tip: For hot tubs or heavy loads, use "Heavy Load" option and consider 6×6 posts regardless of height.
* Values show maximum beam span (distance between posts). Based on No. 2 grade lumber, wet service conditions, L/360 deflection limit.
🏗️ Complete Guide to Deck Post Spacing
Proper deck post spacing is crucial for structural integrity and building code compliance. Whether you're building a new deck or replacing an old one, understanding the relationship between post spacing, beam size, and joist span is essential for a safe and durable structure.
Understanding Post Spacing Rules
The International Residential Code (IRC) 2021 provides prescriptive tables for deck construction. Post spacing depends primarily on beam size and joist span. Larger beams can span further between posts, while longer joist spans require posts to be closer together.
📏 General Spacing Guidelines
4×4 posts: Maximum 6 feet apart, decks ≤5ft high only
6×6 posts: Maximum 8 feet apart, required for taller decks
Railing posts: Maximum 6-8 feet depending on material
Always verify: Check local building codes for your area
Factors Affecting Post Spacing
Several factors influence how far apart your posts can be. Wood species matters significantly - Southern Pine is stronger than SPF lumber. Load requirements also affect spacing - hot tubs and heavy snow loads require closer post spacing or larger beams.
Why Visual Layout Matters
Our calculator provides a visual diagram showing exactly where each post should be placed. This helps you plan your footing locations before digging, ensures even spacing across your deck, and helps identify potential issues with obstructions or uneven ground.
📏 Quick Facts
4×4 Max Spacing: 6 feet
6×6 Max Spacing: 8 feet
Railing Posts: 6 ft max
4×4 Max Height: 5 feet
💡 Pro Tips
• Always dig footings below frost line
• Use post-to-beam connectors
• Set posts in concrete, not on top
• Check posts for plumb before securing
⭐
Bookmark this page
Press Ctrl+D (⌘+D on Mac) for quick access next time.
Deck post spacing depends on beam size, joist span, and wood species. Generally: 1) Determine your joist span (distance from ledger to beam), 2) Choose your beam size from IRC Table R507.5, 3) Find the maximum allowed post spacing for that beam. For example, with 10ft joists and a 2-2×10 beam in Southern Pine, posts can be up to 7'-10" apart.
4×4 posts should typically be spaced no more than 6 feet apart when supporting deck beams. They're limited to decks 5 feet or less in height. For taller decks or wider spacing (up to 8 feet), use 6×6 posts instead. Local building codes may have stricter requirements.
Deck support posts are typically spaced 6 to 8 feet apart, depending on beam size and wood species. The IRC allows up to 8 feet for most configurations with proper beam sizing. For railing posts, the maximum is 6 feet for 4×4 posts and 8 feet for 6×6 posts to meet the 200-lb lateral load requirement.
For a 12-foot beam span (distance between posts) with 10-foot joists: you need at least a 3-2×10 beam in Southern Pine, or 3-2×12 for other species. With shorter joists (6-8 feet), a 2-2×10 or 2-2×12 beam may suffice. Always verify with your local building code.
The number of footings equals the number of posts. Calculate posts needed by: dividing deck length by maximum post spacing (typically 6-8 ft), then multiply by number of beam rows. For a 16×12 deck with one beam: approximately 3 posts per beam × 1 beam = 3 footings, plus corner posts if freestanding.
Maximum deck beam spans per IRC 2021: 2-2×8 can span up to 8'-9" with 6ft joists; 2-2×10 up to 10'-3"; 2-2×12 up to 11'-10". These values are for Southern Pine at 40 PSF. Longer joist spans reduce allowable beam spans. Always use local code tables for your specific lumber species.
🏗️ Disclaimer: This calculator provides estimates based on IRC 2021 guidelines for planning purposes only. Actual requirements may vary based on local building codes, site conditions, and specific project requirements. Always consult with a licensed contractor or structural engineer and verify with your local building department before construction.