When building a deck that’s code-compliant, safe, and cost-efficient, one of the most discussed decisions is picking the right deck post size. Oversized posts drive up your project budget, while undersized posts can risk structural failure. At The Ultimate Deck Shop, we guide homeowners and contractors through this critical decision daily, ensuring decks across Regina, Saskatoon, and beyond balance structural soundness without unnecessary overspending. This guide clarifies how to calculate the proper deck post size by focusing on load, height, and spacing—and how to avoid the costly habit of overbuilding.
The size and type of posts you select impact the safety, longevity, and usability of your outdoor living space. We explain how to evaluate your deck’s needs step-by-step, dispel common myths, and share real-world advice from our team, incorporating best practices recognized by thousands of satisfied customers. Whether you’re a DIYer or a pro, this walkthrough will set the baseline for your project and help you build smart—never just big.
What is Deck Post Size? Definition and Core Factors
“Deck post size” refers to the cross-sectional dimensions—typically 4x4 or 6x6—of the upright support members transferring deck loads from beams down to footings or helical piles. The right choice is dictated by:
- Load: The total weight the post must support, including people (live load), deck material (dead load), and any extras (planters, hot tubs, snow accumulation).
- Height: The vertical distance from ground or footing to the underside of the main deck beam, which influences buckling risk and wind sway.
- Spacing: The distance between each post (commonly 6 to 12 feet), which affects each post’s tributary area—the section of deck surface it supports.
Step-by-Step Guide: Calculating Ideal Deck Post Size
There’s no single "magic number"—the process involves basic math and practical judgement. Here’s how we walk through it at The Ultimate Deck Shop:
- Determine Tributary Area (TA) per Post: For each post, multiply the half-span to each adjacent beam or ledger by the post spacing. For example, a post set 8 feet apart with a beam that supports an 8-foot projection = 8’ × 8’ = 64 sq ft tributary area.
- Calculate Total Load per Post: Multiply TA by the combined design load for your region. Most Canadian codes stipulate 50 psf live load plus 10 psf dead load = 60 psf. Example: 64 sq ft × 60 psf = 3,840 lbs per post.
- Assess Required Footing Size: Divide post load by your soil’s bearing capacity (often 1,500–3,000 psf). This determines your concrete pad or screw pile size. At The Ultimate Deck Shop we offer post bases and Sonotubes to suit these calculations.
-
Find the Minimum Acceptable Post Size: Consult span tables (similar to the one below) or manufacturer span charts for the lumber type you’re using. General rule:
- Up to 6 feet tall and supporting loads up to ~3,000 lbs: 4x4 post.
- 6 to 10 feet tall or supporting >3,000 lbs: 6x6 post, especially if above ground level or for main beams/interior posts.
- Over 10 feet: 6x6 with lateral bracing; check with your local building inspector for requirements.
- Adjust for Local Codes and Real-World Factors: Always check local bylaws or consult professionals for high decks, unusual loads (hot tubs, planters), or ground instability. Our experts at The Ultimate Deck Shop provide complimentary reviews at the planning stage.
Quick Deck Post Sizing Chart
| Post Height (Ground to Beam) | Post Spacing <8 ft | Post Spacing 8-12 ft | Typical Max Load (lbs) |
|---|---|---|---|
| Up to 6 ft | 4x4 | 4x4 or 6x6 | ~3,000 |
| 6–8 ft | 6x6 | 6x6 | 5,000+ |
| 8–10 ft | 6x6 w/bracing | 6x6 or larger | ~7,000 |
Data based on pressure-treated lumber generally carried at The Ultimate Deck Shop. For steel posts, consult us directly for engineered solutions.
Why Not Just Use 6x6 Everywhere? Pitfalls of Overbuilding
While bigger posts feel stronger, defaulting to 6x6 everywhere brings several hidden costs and risks:
- Material cost: 6x6 posts are more expensive than 4x4, often by 30–50%.
- Harder to handle: Heavier posts require more effort and larger base hardware.
- Visual bulk: Oversized posts can look clumsy on low or smaller decks.
- Not always better: For spans under 7 feet and heights under 6 feet, 4x4 supports are fully code-compliant with correct installation.
Best practice: size your posts for the actual loads, not the "biggest possible." Our team can help review your deck plan to flag any spots where you can safely use a 4x4, especially along perimeter rails and steps.
Common Real-World Scenario: Two-Height Deck Example
Consider a 12x20 ft deck split into a 4-foot and an 8-foot section, which is common in Canadian yards with sloped terrain. The shorter section’s posts support a smaller tributary area; here, 4x4 posts can be safely installed, provided spacing is within 8 feet. For the taller portion (8 ft), main structural or interior posts benefit from switching to 6x6 for better resistance to flex and wind wobble. We’ve supplied hundreds of decks in Regina and Saskatoon using this blended approach, saving customers on lumber without sacrificing code or stability. For more on hybrid framing, see our in-depth guide to buying deck materials online.
Critical Considerations: Wind, Soil, and Footing Choices
Deck stability isn’t just about vertical strength. High decks or those exposed to prairies winds need stiffer posts (often 6x6) or additional lateral bracing. Soil can be equally important—clay or silt may settle more than gravel or sand, impacting footing stability. Our experts at The Ultimate Deck Shop can help assess local conditions or recommend helical/screw pile accessories for tough soils. Proper sizing also lets you reduce the total post count by slightly increasing size or improving footing details, leading to a cleaner, safer design.
Best Practices for Building Code and Inspector Approval
- Check local code: Most require 4x4 as the minimum, but may demand 6x6 above 6’ in height or for stair guard posts.
- Don’t mix grades: Use only structural/lumber-grade posts for substructures.
- Fastening matters: Attach with hardware-rated post bases—Simpson Strong-Tie and Fortress options are in stock at TUDS.
- Protect for longevity: Apply joist tape or deck frame sealers to prevent rot, especially at ground contact. For tough climates, consider Fastenmaster Deck Frame Coating.
Fastenmaster Deck Frame Coating
Post Maintenance: Keeping Your Supports Solid for Decades
Maintaining posts means more than choosing the right size up front. Annual inspections for rot, moisture wicking, or soil shift keep your structure safe for the long term. For season-long advice—cleaning stains, sealing cracks, and more—use our comprehensive Deck Maintenance resource. We recommend routine care especially for wood, including cleaning with products such as TUDS SUDS Deck Cleaner and re-sealing as needed.
Tools and Tech: Take the Guesswork Out
- Deck Budget Calculator for estimating material costs and quantities.
- Professional-grade GH Leveller for fast height checks, available in store.
GH Leveller - Rent or purchase installation tools, plus get support at every build stage—our knowledgeable staff is known for real-world deck experience and a hands-on approach.
Frequently Asked Questions
How do I know if I can use 4x4 posts instead of 6x6?
As a baseline, 4x4 posts are suitable up to 6 feet tall and for posts spaced no farther than 8 feet, supporting typical loads (roughly up to 3,000 lbs). For heights above 6 feet, switch to 6x6 unless an engineer or local inspector states otherwise.
Can I mix 4x4 and 6x6 posts on the same deck?
Yes, and it is often best practice. Use 6x6 for main structural/interior posts or tall sections, and 4x4 for perimeter or lower height sections. This saves money yet stays code-compliant.
What happens if I undersize my posts?
Undersized posts can result in deck flex, lateral sway, or, in extreme cases, vertical collapse. Local building inspectors may also fail your project, adding costly delays and fixes.
Is steel decking post framing an option?
Yes; steel framing offers higher strength for long spans or commercial decks. Consult with The Ultimate Deck Shop for engineered steel options for your design.
How do I maintain deck posts so they don’t rot?
Annual inspection, cleaning, and applying a deck sealer or frame coating can extend wood post life dramatically. For in-depth tips, visit our Deck Maintenance page. If you notice soft spots or cracking, replace the affected post promptly.
Does The Ultimate Deck Shop deliver posts and hardware?
Yes. We offer delivery within Saskatchewan and ship Canada/US-wide for most products. Our experienced crew ensures materials arrive organized for easy build sequencing.
Summary: Build Smart with The Ultimate Deck Shop
Choosing the optimal deck post size protects your investment, meets code, and keeps your deck sturdy for decades. Always size posts to your unique load, height, and layout rather than defaulting to the biggest (and priciest) option. If you need personalized advice, reach out to The Ultimate Deck Shop for in-store or virtual consultations. Our extensive experience in Saskatchewan’s climate, combined with our customer-first approach, makes us the trusted source for deck materials, planning, and year-round support.
Ready to plan or upgrade your deck? Try the Deck Budget Calculator, or visit us in Regina and Saskatoon for pressure-treated posts, hardware, and expert recommendations for decks that last in any season.
And don’t forget: Proper post maintenance protects your structure for years. Regular care, cleaning, and seasonal checks can prevent costly repairs—explore our Deck Maintenance guide and see why thousands trust us to keep their outdoor spaces safe and beautiful.
