Wood Board Sizes Chart in Construction in USA

Understanding Nominal vs. Actual Wood Board Sizes

In U.S. construction, lumber is typically sold using nominal dimensions, such as 2×4, 2×6, or 1×12. However, the actual size of these boards is smaller due to the planing and drying processes after the initial cut. The nominal size represents the board’s size before it is surfaced. Understanding the difference between nominal and actual dimensions is critical for accurate planning, material estimation, and structural integrity in all phases of construction.

Dimensional Lumber Used in Framing

2×4 Boards

2×4 lumber is one of the most widely used sizes in residential framing. Its actual dimensions of 1-1/2 x 3-1/2 inches make it ideal for wall studs, headers, and floor plates. In standard wall construction, 16-inch on-center spacing is typical when using 2×4 studs for adequate support and insulation capacity.

2×6 Boards

2×6 lumber offers more load-bearing strength and insulation space. With actual dimensions of 1-1/2 x 5-1/2 inches, it’s commonly used for exterior walls, roof rafters, and joists where increased thermal performance or structural capacity is needed.

2×8 and 2×10 Boards

These larger boards, measuring 1-1/2 x 7-1/4 inches for 2×8, and 1-1/2 x 9-1/4 inches for 2×10, are frequently found in floor joist systems, deck framing, and roof construction. Their increased depth allows for greater spanning distance and structural rigidity.

Non-Structural Wood Board Sizes for Interior Finishes

1x Boards

Boards such as 1×4, 1×6, and 1×12 are primarily used for interior finishes, trim, baseboards, casing, and shelving. With their actual 3/4-inch thickness, they are ideal for applications that require flatness, clean appearance, and dimensional stability.

1×2 and 1×3 Boards

1×2 and 1×3 boards serve well in decorative trim, paneling, furring strips, and craft applications. Their narrow width and light weight make them easy to manipulate and install with basic carpentry tools.

Treated Lumber Sizes and Their Applications

Pressure-Treated 2×4 and 2×6 Boards

For outdoor construction, such as decks, fences, and landscape framing, pressure-treated wood is standard. Sizes like 2×4 and 2×6 in treated formats maintain the same actual dimensions as their untreated counterparts but are chemically treated to resist moisture, rot, and insects.

Deck Boards

5/4 decking boards, often marketed as 5/4 x 6, are a popular size for decking surfaces. Their actual dimensions are 1 inch thick by 5-1/2 inches wide, offering a balance between strength and comfort underfoot.

Plywood and Sheet Goods Standard Sizes

Although not classified as board lumber, sheet goods are crucial in U.S. construction. The standard plywood sheet size is 4 feet by 8 feet (48 x 96 inches), available in thicknesses like 1/4″, 3/8″, 1/2″, 5/8″, and 3/4″. These are often used for subflooring, sheathing, and underlayment.

Hardwood Boards for Finish Carpentry

Nominal Sizing for Hardwoods

Unlike softwoods, hardwood boards are often sold in actual sizes or by thickness in quarters, such as:

• 4/4 (1 inch)
• 5/4 (1.25 inches)
• 6/4 (1.5 inches)
• 8/4 (2 inches)

Widths and lengths vary and are often random, depending on milling and species.

Custom Milled Hardwood Sizes

Custom cabinetry, built-ins, and fine woodworking may require custom milled boards, particularly in high-end residential and commercial builds. The builder selects the thickness and width based on design specs and aesthetic needs.

Moisture Content and Dimensional Stability

All wood board sizes can be affected by moisture levels. Boards are typically dried to a moisture content of 19% or less, labeled as S-DRY or KD-HT (kiln dried and heat treated). Proper drying minimizes shrinkage, warping, and cupping during and after installation.

Visual and Structural Grades in Dimensional Lumber

Visual Grades

Softwoods like Douglas Fir, Southern Yellow Pine, and Hem-Fir are graded visually based on knot size, grain orientation, and defects. Higher grades such as Select Structural or #1 Common offer superior appearance and strength.

Machine Stress-Rated Lumber

Used for engineered applications, MSR lumber is graded mechanically to ensure precise load capacities and is often required for floor joists, roof trusses, and multi-story framing systems.

Engineered Wood Dimensions

LVL and Glulam

Laminated Veneer Lumber (LVL) and glulam beams come in standardized depths such as 9-1/2″, 11-7/8″, and 14″, used for beams, headers, and load-bearing applications. These engineered products provide dimensional consistency, longer spans, and superior strength-to-weight ratios.

I-Joists

Engineered I-Joists feature standardized flange sizes and depths such as 9-1/2″, 11-7/8″, and 14″, used for floor systems in residential and commercial builds. These allow for greater spans and reduce construction material costs while improving performance.

Conclusion

The wood board sizes chart in U.S. construction serves as an essential reference point for architects, builders, and contractors. By understanding the differences between nominal and actual dimensions, selecting the correct size for specific applications, and accounting for grade, moisture content, and treatment, we ensure efficient, durable, and code-compliant construction practices across every project.