Dimension Lumber Sizes Chart in Construction in USA

Understanding Dimension Lumber in U.S. Construction

In the United States construction industry, the term dimension lumber refers to lumber that is cut to standardized widths and depths, specified in nominal sizes such as 2×4, 2×6, and 4×4. These dimensions are used extensively in framing, structural work, and finish carpentry. However, the actual size of these boards is smaller than their nominal dimensions due to the planing process that smooths the wood after it has been rough cut.

Standard Dimension Lumber Sizes Chart

The following chart displays the most common nominal sizes of dimension lumber used in construction, alongside their actual sizes in inches.

These are the typical dimensions for surfaced (S4S) lumber, which has been planed on all four sides.

Lumber Categories by Thickness

Lumber in the United States is categorized by its thickness range as follows:

• Boards: Less than 2 inches thick (e.g., 1×4, 1×6)
• Dimension Lumber: 2 to 5 inches thick (e.g., 2×4, 2×6)
• Timbers: More than 5 inches thick (e.g., 6×6, 8×8)

Understanding this classification helps determine how a piece of lumber will be used in residential, commercial, or industrial construction.

Most Common Dimension Lumber Sizes in Framing

2×4 Lumber

• Actual Size: 1½ x 3½ inches
• Primary Uses: Wall studs, interior framing, partition walls

2×6 Lumber

• Actual Size: 1½ x 5½ inches
• Primary Uses: Exterior wall framing, floor joists, roof rafters

2×8 Lumber

• Actual Size: 1½ x 7¼ inches
• Primary Uses: Floor joists, ceiling joists, headers

4×4 Lumber

• Actual Size: 3½ x 3½ inches
• Primary Uses: Posts, columns, exterior supports

6×6 Lumber

• Actual Size: 5½ x 5½ inches
• Primary Uses: Load-bearing beams, deck posts, structural supports

Dimension Lumber Lengths

In the United States, dimension lumber is sold in standard lengths including:

• 6 ft
• 8 ft
• 10 ft
• 12 ft
• 14 ft
• 16 ft
• 18 ft
• 20 ft

Lengths are usually in 2-foot increments, with 16-foot and 20-foot boards common for floor joists and roof trusses.

Moisture Content and Surfacing Impact on Size

S4S (Surfaced Four Sides) Lumber

Most dimension lumber sold in U.S. retail outlets is S4S, meaning it is planed smooth on all four sides. This surfacing process removes approximately ¼ inch from each side, reducing the actual dimensions from the rough-cut nominal size.

Green vs. Kiln-Dried

• Green lumber: Cut fresh and may shrink after installation
• Kiln-dried lumber: Dried to a stable moisture content, usually 19% or less (KD-19), which helps prevent warping, twisting, and splitting

Structural Grade and Stress Rating

Dimension lumber is also graded based on structural integrity. The grading system includes:

• Select Structural: Highest quality, minimal defects
• No.1 and No.2: Common for framing and structural applications
• Construction Grade: Budget-friendly, moderate knots and imperfections

Stress ratings such as Fb (bending strength) and E (modulus of elasticity) are critical in selecting the correct dimension lumber for load-bearing structures.

Species of Wood Used for Dimension Lumber

Dimension lumber is produced from a variety of softwood species, each with specific applications:

• Douglas Fir: Strong, stable, ideal for framing
• Southern Yellow Pine: Dense and durable
• Hem-Fir: Lightweight, versatile
• Spruce-Pine-Fir (SPF): Economical, common in studs and light framing
• Redwood and Cedar: Preferred for outdoor applications due to natural resistance to decay

Markings and Stampings on Dimension Lumber

Every piece of graded lumber in the U.S. carries a grade stamp, which includes:

• Mill number
• Grade of wood
• Moisture content (e.g., KD-19)
• Species group
• Certification agency

This information is essential for verifying the suitability of lumber for a given structural role in residential or commercial buildings.

Buying Tips for Accurate Dimension Lumber Sizes

To ensure you’re purchasing the correct material:

• Verify actual size by measuring before purchase
• Inspect for warping, bowing, or splits
• Choose the proper grade for your project
• Confirm moisture content if using indoors
• Buy from reputable lumberyards for quality assurance

Conclusion

Dimension lumber sizes in the United States construction industry are based on a standardized nominal system that simplifies communication but differs from the actual size due to sawing and surfacing. For professionals in construction, understanding these sizes, their specific applications, structural ratings, and material properties is essential for ensuring safe, efficient, and code-compliant builds. Whether building frames, decks, roofs, or interiors, choosing the correct dimension lumber is critical to the structural integrity and longevity of every project.