6×6 Post Actual Size in Construction in USA

Understanding the Nominal vs. Actual Size of a 6×6 Post

In U.S. construction standards, the term “6×6 post” refers to the nominal dimensions of lumber, which are not the actual physical measurements. Due to the surfacing and finishing process, the actual size of a 6×6 post is 5.5 inches by 5.5 inches. This industry-wide practice ensures consistency across building materials and framing practices.

• Nominal Size: 6 inches by 6 inches
• Actual Size: 5.5 inches by 5.5 inches (139.7 mm x 139.7 mm)

This reduction of 0.5 inches on each side is the result of planing, which smooths the lumber after it is initially cut. This is standard for dimensional lumber sold for structural purposes in the USA.

Common Species Used for 6×6 Posts

6×6 lumber is available in a variety of wood species, each offering unique properties suited to different construction environments:

• Douglas Fir: Known for high structural strength and dimensional stability
• Southern Yellow Pine: Common for pressure-treated posts, especially for exterior use
• Hem-Fir: Used in interior structural framing
• Cedar and Redwood: Chosen for aesthetic value, natural decay resistance, and exterior applications

Standard Lengths and Availability of 6×6 Posts

6×6 posts are widely available in the following standard lengths:

• 8 feet
• 10 feet
• 12 feet
• 14 feet
• 16 feet
• 20 feet

Custom cuts may also be ordered through specialty lumberyards for architectural columns, load-bearing supports, or deck footings. The uniform cross-sectional dimension of 5.5” x 5.5” remains consistent across all lengths.

Typical Applications of 6×6 Posts in U.S. Construction

1. Structural Load-Bearing Columns

In residential and commercial buildings, 6×6 posts are commonly used as vertical structural elements that bear heavy axial loads. Applications include:

• Basement support columns
• Garage beams and headers
• Porch and patio posts
• Load-bearing walls with large spans

These posts often support LVL beams, steel girders, or roof trusses, requiring precise sizing and alignment.

2. Deck Posts and Exterior Framing

For deck construction, 6×6 posts are the industry standard for:

• Deck support footings
• Pergola columns
• Covered porch framing
• Stair landings

Pressure-treated 6×6 posts offer superior stability over 4x4s and are typically anchored in concrete piers or secured with post bases rated for structural loads.

3. Fencing and Gate Construction

6×6 posts are often selected for gate hinges, corner fence supports, and entryways in privacy fencing due to their resistance to flex and long-term durability.

• Heavy gates
• Double-entry driveways
• Horse corral posts

Treated or naturally decay-resistant woods such as cedar are preferred in these exposed applications.

Weight and Handling of a 6×6 Post

The weight of a 6×6 post depends on the length, species, and moisture content. Below is a general estimation:

• 6×6 x 8 ft (Southern Pine, dry): ~70 lbs
• 6×6 x 12 ft (Douglas Fir, dry): ~100 lbs
• 6×6 x 16 ft (pressure-treated): ~130–150 lbs

Due to their substantial mass, 6×6 posts often require two-person handling, especially for installation at height or when working with overhead beams.

Pressure-Treated 6×6 Posts for Outdoor Use

For exterior applications, 6×6 posts must be pressure-treated with chemicals to protect against:

• Termite damage
• Fungal decay
• Moisture exposure

Most commonly used treatments include:

• Alkaline Copper Quaternary (ACQ)
• Copper Azole (CA-C)
• Micronized Copper Azole (MCA)

Treated posts are generally rated for ground contact or above-ground use, depending on their chemical retention level. Proper labeling and AWPA certification are essential when sourcing treated lumber.

Load-Bearing Capacity of a 6×6 Post

The load capacity of a 6×6 post depends on various factors including:

• Species and grade
• Height of unsupported length
• End condition (fixed vs. pinned)
• Load type (axial, lateral, combined)

For reference, a 6×6 Douglas Fir No. 1 post can typically support:

• Over 20,000 lbs of axial load when less than 10 feet tall
• Up to 13,000–15,000 lbs under typical deck footing conditions

Engineering calculations or prescriptive tables from the IRC should be used for accurate load planning.

6×6 Post Installation Techniques

To maintain structural integrity, proper installation practices are critical:

• Anchor posts with concrete or metal brackets to prevent lateral movement
• Use hot-dip galvanized or stainless steel hardware for treated lumber
• Ensure level and plumb placement before fastening
• Brace posts during curing of concrete footings

Misaligned posts can cause structural failures, especially under wind or seismic loads.

Cost of a 6×6 Post Based on Market Trends

Pricing for 6×6 posts varies depending on material, treatment, and region:

• Untreated SPF 6×6 x 8 ft: $25–$40
• Pressure-treated 6×6 x 10 ft: $45–$70
• Cedar 6×6 x 10 ft: $80–$120
• Redwood 6×6 x 12 ft: $150+

Bulk orders, such as those required for large decks, fence lines, or structural framing, often come with volume discounts.

Fire Ratings and Code Compliance for 6×6 Posts

In fire-rated construction, 6×6 posts can be incorporated into 1-hour or 2-hour assemblies when paired with:

• Fire-resistant coatings or wraps
• Type X gypsum enclosures
• Specified clearances and chases

The International Building Code (IBC) and International Residential Code (IRC) dictate usage based on seismic zone, wind load, and exposure conditions.

Conclusion

The 6×6 post, with an actual dimension of 5.5 inches by 5.5 inches, is a foundational element in residential and commercial construction across the United States. Offering exceptional load-bearing capacity, dimensional stability, and durability, it plays a vital role in applications ranging from deck footings to support columns, architectural features, and outdoor framing. Whether pressure-treated or naturally rot-resistant, the 6×6 remains a trusted choice for builders aiming for strength, longevity, and compliance with modern building codes.