Home Improvement Skills & Specialties Tools & Materials

Dimensional Lumber Sizes for Building and Remodeling

By
Lee Wallender
Lee Wallender
Lee Wallender

Lee has over two decades of hands-on experience remodeling, fixing, and improving homes, and has been providing home improvement advice for years.

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Updated on 03/09/24
Reviewed by
Deane Biermeier
Deane Biermeier
Reviewed by Deane Biermeier
Deane Biermeier is an expert contractor with nearly 30 years of experience in all types of home repair, maintenance, and remodeling. He is a certified lead carpenter and also holds a certification from the EPA. Deane is a member of The Spruce's Home Improvement Review Board.
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Fact checked by
Jillian Dara
Jillian Dara
Fact checked by Jillian Dara
Jillian is a freelance journalist with 10 years of editorial experience in the lifestyle genre. She is a writer and fact checker for TripSavvy, as well as a fact-checker for The Spruce.
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Illustration showing common dimensional lumber sizes

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In This Article

Dimensional lumber has two size categories for width and thickness: nominal size and actual size. Dimensional lumber is wood lumber that is cut to pre-defined, standard sizes. A two-by-four (or, 2x4) is an example of dimensional lumber. Nominal is the stated name (2x4, for example), and actual refers to the physical dimensions (1-1/2 inches by 3-1/2 inches).

Nominal Size vs. Actual Size

Dimensional lumber has differing nominal and actual width dimensions—for the same-sized board. Because of the thickness of the saw blade and other milling processes, the resulting two-by-four does not measure 2 inches by 4 inches. Instead, it is 1-1/2 inches by 3-1/2 inches.

  • Nominal size: Nominal size lumber has a given name, but this is only a nickname for the width of the board. Two-by-four (or 2x4) is the name of the board, not its measurements. Physically, the board's width measures 1-1/2 inches by 3-1/2 inches.
  • Actual size: Actual size is as if you were using a tape measure or a straight edge to measure the width of the board.

Tip

In rare cases, nominal and actual dimensions will match. Some older homes may have nominal dimension two-by-fours that measure 2 inches by 4 inches. It's not common, but you may find this when remodeling a home. While it's tempting to want to reuse this stock for other applications around the house, it can be difficult, unless those other areas also use the older type.

Dimensional Lumber Sizing

Softwoods used for building framing have the following nominal and actual dimensions. These dimensions do not apply to laminated veneer lumber boards, hardwoods, or floorboards. Softwoods include woods such as Douglas fir, spruce, or Hem-Fir (a mixture of Western Hemlock and Amabilis Fir).

Nominal Size Actual Size
1×2 3/4 x 1-1/2
1×3 3/4 x 2-1/2
1×4 3/4 x 3-1/2
1×6 3/4 x 5-1/2
1×8 3/4 x 7-1/4
1×10 3/4 x 9-1/4
1×12 3/4 x 11-1/4
2×2 1-1/2 x 1-1/2
2×3 1-1/2 x 2-1/2
2×4 1-1/2 x 3-1/2
2×6 1-1/2 x 5-1/2
2×8 1-1/2 x 7-1/4
2×10 1-1/2 x 9-1/4
2×12 1-1/2 x 11-1/4
4×4 3-1/2 x 3-1/2
4×6 3-1/2 x 5-1/2
4×8 3-1/2 x 7-1/4
4×10 3-1/2 x 9-1/4
4×12 3-1/2 x 11-1/4

Decking Planks

Unlike dimensional lumber for building, decking planks come in just a few sizes:

Nominal Size Actual Size
5/4 x 6 1-inch x 5-1/2 inches
2 x 4 1-1/2 inches x 3-1/2 inches
2 x 6 1-1/2 inches x 5-1/2 inches
2 x 8 1-1/2 inches x 7-1/2 inches

To convert square footage into linear footage, use this formula:

(Square footage x 12) / board width = linear footage

For example, to convert 100 square feet into linear footage for 4-inch-wide boards:

(100 x 12) / 4 = 300 linear feet.

Dimensional Lumber Lengths

With dimensional lumber, dimensions refer to the width and depth. So, a dimensional two-by-four (2x4) board can be 12 feet long, for example, but that length is not figured into the dimensions. The length is treated separately.

Lengths typically are shown as the last number. A typical dimensional lumber designation might read as such: "2 in. x 4 in. x 8 ft."

This can be confusing because it is a mixture of nominal and actual sizes. The first two numbers (2 inches and 4 inches) are nominal widths and depths for the lumber. As stated earlier, their actual sizes are 1-1/2 inches and 3 -/2 inches.

Yet lengths of dimensional stock are always expressed as actual sizes. So, this example board's actual length is 8 feet. When you take that "2 in. x 4 in. x 8 ft." board home, it will measure out to be 1-1/2 inches by 3-1/2 inches by 8 feet.

Dimensional Lumber Basics

Dimensional lumber is sawn, planed, and sometimes further smoothed to standard sizes. Standardization means that all builders and do-it-yourselfers are using lumber that is sized the same way.

  • Lumber that is cut to standard widths and depths, but never lengths.
  • Typical dimensional lumber: two-by-fours (2x4) and two-by-sixes (2x6).
  • Sheet goods, though cut to standard sizes, are not dimensional lumber.
  • Nominal and actual dimensions differ.
  • Older homes may have lumber with nominal and actual dimensions that match.

Dimensional Lumber and Modern Building

As early as the 1870s, lumberyards began to use the now-familiar two-by-four (2x4) or two-by-six (2x6) designations for dimensional lumber. But it wasn't until the 1920s that the term dimensional lumber came into popular use to distinguish lumber cut to pre-determined sizes from other types of wood, such as corded wood for fireplaces.

During this period, the building industry sought to control costs and minimize waste by developing standard sizes and grades for building timber. Most significant, though, was the rapid change from the post-and-beam style of house framing to the more efficient balloon framing style.

It is rarely necessary to use the term dimensional lumber when shopping for building materials. All lumber you will buy at lumber yards or home centers will be already cut to pre-determined sizes.

For the average do-it-yourselfer, most long, thin lumber that will be used for building is considered to be dimensional lumber.

Other types of lumber, such as plywood and other sheet goods, are offered in prescribed standard sizes but are not referred to as dimensional lumber.

FAQ
  • What is the most common size of dimensional lumber?

    The most common size of dimensional lumber is the two-by-four (or, 2x4), which measures 1-1/2 inches by 3-1/2 inches. Four-by-fours (4x4) are typically used as fence posts.

  • What is dimensional lumber used for?

    Dimensional lumber is used for building. Because dimensional lumber is standardized, it can be used for building or remodeling homes.

  • What dimensional lumber size do I need?

    The type of dimensional lumber you need is dictated by the application. When building or remodeling homes, two-by-fours are typically used for walls. Two-by-sixes or two-by-eights are often used for floor joists or ceiling rafters.

  • Are there any limitations to using dimensional lumber?

    Yes, there are limitations to using dimensional lumber. Older types may not be compatible with newer wall systems, making them difficult to reuse. When replacing load-bearing walls, laminated veneer lumber (LVL) or engineered beams are needed for proper support, as regular dimensional lumber may not be strong enough. Additionally, there are recommended spans between wall supports for different sizes of dimensional lumber and thickness requirements for shelving made from particleboard.

  • Which wood species are available in dimensional lumber?

    Dimensional lumber includes a wide variety of wood species to choose from, such as pine, poplar, cedar, fir, walnut, alder, and birch. Cedar is a good option as it is both affordable and ages well due to its natural oils. However, softwoods like pine and poplar deteriorate quickly if left untreated and must be painted or stained. Expensive hardwoods like walnut and mahogany age well but are more costly.