Deck Post Spacing Calculator
Post Spacing & Cost
6 ft spacing
Max beam span: 8 ft (Doubled 2×10)
Posts Needed
3
Post Spacing
6 ft
Footings
3
Post + Footing Cost
$174 – $495
Beam Span
12 ft
Tip: Beam cantilever past the outer posts cannot exceed 1/4 of the span between posts. For example, with 8 ft spacing, max cantilever is 2 ft on each end.
Footings: Concrete footings must extend below the frost line (24–48″ in northern states, 12–18″ in southern states). Typical footing diameter is 12″ for 4×4 posts and 16″ for 6×6 posts.
IRC Reference: Post spacing and beam spans are per IRC Table R507.5 (40 PSF live + 10 PSF dead load). Always verify requirements with your local building department, as local codes may be more restrictive.
Disclaimer: Estimates are for budgeting purposes only. Actual costs vary by location, contractor, material availability, and project complexity. Always get professional quotes for exact pricing.
Deck Post Spacing Reference
| Beam Size | Max Span Between Posts |
|---|---|
| Doubled 2×8 | 6 ft |
| Doubled 2×10 | 8 ft |
| Doubled 2×12 | 10 ft |
| 3-Ply 2×10 | 10 ft |
| 3-Ply 2×12 | 12 ft |
* Per IRC Table R507.5 at 40 PSF live + 10 PSF dead load. #2 grade lumber.
Post + Footing Cost Per Post
| Post Size | Ground Level | Elevated 4–6 ft | Elevated 6–10 ft |
|---|---|---|---|
| 4×4 PT | $58 – $165 | $59 – $167 | $60 – $170 |
| 6×6 PT | $65 – $180 | $67 – $185 | $70 – $189 |
* Includes post lumber and concrete footing ($50–$150 per footing). Elevated decks have a multiplier on post cost for longer lumber.
How We Calculate
Our deck post spacing calculator determines post count, spacing, and cost based on deck dimensions, beam size, post size, and deck height. Spacing is constrained by the beam's maximum span per IRC Table R507.5.
How the math works: Number of spans = deck length ÷ max beam span (rounded up). Posts per beam = spans + 1. Actual spacing = deck length ÷ number of spans. Cost includes posts (with height multiplier) and concrete footings ($50–$150 each).
IRC Beam Span Table
Maximum span between posts per IRC R507.5 at 40 PSF live + 10 PSF dead load: Doubled 2×8 (6′), Doubled 2×10 (8′), Doubled 2×12 (10′), 3-Ply 2×10 (10′), 3-Ply 2×12 (12′). These are conservative values for #2 grade lumber.
Post Size Guide
4×4 PT posts ($8–$15 each) are suitable for ground-level decks under 4 ft. 6×6 PT posts ($15–$30 each) are required for elevated decks, longer post heights, and heavier loads. Building codes in most jurisdictions require 6×6 posts for decks 4+ ft above grade.
Footing Requirements
Each post requires a concrete footing ($50–$150 each) extending below the frost line. Typical footings use 12″ or 16″ Sonotube forms filled with concrete. Footings must rest on undisturbed soil and be sized for the tributary load they support.
Cantilever Rules
Beams can cantilever past the outer posts up to 1/4 of the span between posts. For example, with 8 ft post spacing, the beam can overhang up to 2 ft on each end, reducing the total number of posts needed.
Data Sources
Beam spans per IRC R507.5 (2021 International Residential Code). Post and footing costs compiled from Home Depot, Lowe's, and contractor estimates (February 2026).
Last updated: 2026-02-04
Frequently Asked Questions
What is the standard deck post spacing? +
Standard deck post spacing is 6–8 feet apart, determined by the beam size. Doubled 2×8 beams allow 6 ft max spacing, Doubled 2×10 beams allow 8 ft, and Doubled 2×12 beams allow 10 ft between posts. Spacing must comply with IRC Table R507.5 for your specific beam and load configuration.
When should I use 4×4 vs 6×6 posts? +
Use 4×4 posts for ground-level decks under 4 ft high with standard loads. Use 6×6 posts for elevated decks over 4 ft, decks supporting heavy loads (hot tubs, large groups), or when required by local building codes. Most jurisdictions require 6×6 posts for any deck over 4 ft above grade.
How deep should deck footings be? +
Footings must extend below the local frost line: 24–48 inches in northern states, 12–18 inches in southern states. Typical footing diameter is 12″ for 4×4 posts and 16″ for 6×6 posts. Footings must rest on undisturbed or compacted soil. Always check your local frost line depth with the building department.
What is the maximum beam span between posts? +
Per IRC Table R507.5 (40 PSF live + 10 PSF dead): Doubled 2×8 spans up to 6 ft, Doubled 2×10 up to 8 ft, Doubled 2×12 up to 10 ft, 3-Ply 2×10 up to 10 ft, and 3-Ply 2×12 up to 12 ft between posts. These spans assume #2 grade lumber.
Do I need a permit for a deck? +
Most jurisdictions require a building permit for any attached deck and any freestanding deck over 30 inches above grade. Permit fees range from $75–$500. The permit process typically requires a site plan, structural drawings, and inspections of footings, framing, and railing.
How are deck loads calculated? +
Residential decks are designed for 40 PSF live load (people, furniture) plus 10 PSF dead load (the deck's own weight) = 50 PSF total. Hot tubs require additional engineering (150+ PSF). The total load determines beam size, joist span, post spacing, and footing size.
Should deck posts be notched or bolted? +
Bolted connections are preferred for strength. Notching weakens the post and reduces its load capacity. If notching is required, never notch more than 50% of the post depth and only notch 6×6 posts. Through-bolted connections with carriage bolts or structural connectors (Simpson post caps) are recommended.
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