Actual Size of 6×6 Post in Construction in USA

In American construction, the 6×6 post is a common component used for a variety of structural and architectural purposes. From deck supports, fence posts, load-bearing columns, to timber framing, the 6×6 is prized for its strength and stability. However, it’s essential to recognize that the actual size of a 6×6 post is not exactly six inches by six inches. Due to standard milling and finishing processes, there is a significant reduction from the nominal dimensions. Understanding this difference is vital for accurate project planning, material procurement, and code compliance.

What Is the Nominal vs Actual Size of a 6×6 Post?

A nominal 6×6 post refers to the size before the wood is planed or smoothed. After this process, the actual size is reduced.

Actual Dimensions of a 6×6 Post:

• Nominal Size: 6 inches × 6 inches
• Actual Size: 5.5 inches × 5.5 inches

This reduction of 0.5 inches on each side is standard across all dimensional lumber in the United States, including other sizes like 2×4, 4×4, and 2×6.

Why Does the 6×6 Post Shrink in Size?

The lumber goes through surfacing (S4S – surfaced four sides) at the mill to remove rough edges and to standardize dimensions. During this process:

• The raw timber is dried, causing shrinkage.
• The board is planed smooth, reducing thickness and width.
• Final output is the actual size used in construction drawings and installations.

Common Uses of Actual 6×6 Post in Construction

The 5.5″ x 5.5″ actual size of the 6×6 post provides a balance between strength, durability, and load capacity, making it ideal for:

1. Structural Support Posts

• Load-bearing columns in porches and decks
• Supports under beams or girders
• Foundation posts in pier and beam construction

2. Deck Construction

• Used as vertical posts to hold up elevated decks
• Typically spaced 6 to 10 feet apart
• Anchored to concrete footings using post bases or brackets

3. Pergolas and Outdoor Structures

• As vertical supports for pergolas, gazebos, and patio roofs
• Often left exposed and decoratively finished

4. Fence and Gate Posts

• Installed for tall fences and heavy gates where added strength is required
• Driven deep or set in concrete for stability

Weight and Strength of a 6×6 Post

The actual weight of a 6×6 post depends on the wood species, moisture content, and length. Here’s a general estimate:

• Pressure-treated southern pine (green):
  Approx. 5.5 lbs per linear foot
• A 10-foot long 6×6 post:
  Weighs approximately 55–60 pounds

In terms of structural strength, a 6×6 post provides excellent compressive strength and bending resistance, often used in scenarios where 2×4 or 4×4 posts would be insufficient.

Standard Lengths and Availability

6×6 posts are commonly available in the following lengths:

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

Longer lengths may be available at specialty suppliers, particularly for timber framing projects or custom installations.

Species and Types of 6×6 Posts

1. Pressure-Treated Lumber

• Most widely used for exterior applications
• Treated with preservatives to resist rot, fungus, and termites
• Typically made from southern yellow pine

2. Cedar

• Naturally decay-resistant
• Lighter than pressure-treated
• Popular for decorative outdoor posts

3. Redwood

• Similar to cedar, with superior natural resistance
• Ideal for premium outdoor aesthetics

4. Douglas Fir

• Frequently used for interior load-bearing
• Known for dimensional stability and high strength

5. Engineered Lumber

• Glued laminated timber (Glulam) and LVL beams for advanced applications
• Custom sizes with superior strength-to-weight ratio

Installation Considerations for 6×6 Posts

Proper installation ensures structural stability and compliance with building codes.

1. Anchoring

• Use post bases or brackets rated for the load type
• Anchor to concrete footings using expansion bolts or epoxy

2. Fastening

• Use hot-dip galvanized or stainless steel fasteners to avoid corrosion
• For outdoor use, apply sealant or stain to exposed ends

3. Spacing and Load Calculations

• Must comply with local building codes
• Consider live and dead loads, wind uplift, and snow load

Measuring and Planning with Actual 6×6 Size

When using 6×6 posts in structural drawings or planning, always calculate with the actual size:

• For beam notching, allow for 5.5” width
• For spacing holes or anchors, base them on 5.5” post thickness
• Trim and join other lumber to match actual post dimensions

Accurate measurements prevent errors in cutting, placement, and framing alignment.

Code Requirements for 6×6 Posts in the USA

Building codes, such as those governed by the International Residential Code (IRC), require specific sizing and anchoring for structural posts.

Examples of Code Guidelines:

• Decks over 30 inches high must have guardrails and properly anchored 6×6 posts
• Posts must be supported by minimum 12-inch diameter concrete footings (check regional frost depth)
• Minimum 6×6 post required for decks over 8 feet in height

Always consult local codes and inspectors before installation to ensure full compliance.

Conclusion

The actual size of a 6×6 post in construction in the USA is 5.5 inches by 5.5 inches, despite its nominal label. This dimensional reality is crucial for precise planning, correct structural support, and seamless integration with other building materials. Whether used in deck framing, fencing, or load-bearing construction, understanding and accounting for the actual dimensions of the 6×6 post ensures strength, compliance, and professional execution in every project.