January 9, 2023
So, you wanted to jumpstart your woodworking career and researched the wood dimensions available in the market today. To your surprise, you had come face-to-face with terms like nominal size and actual size of lumber—terms you are pretty unfamiliar with. Things suddenly become confusing to you, and you want to know the difference between nominal and actual lumber sizes.
You might be buying lumber with a nominal size of 2″ x 4″, which is precisely the dimensions of lumber you need for your project. But when you got home and measured the actual dimensions of the lumber, you discovered that its precise measurement was 1.5″ x 3.5.” You wanted to cuss, feeling the wood supplier hoodwinked you by giving you a lumber short of 2×4 inches. Yet, as an aspiring woodworker, it helps to know that the actual lumber dimensions are different from the nominal dimensions of the lumber.
Dimensional Lumber and Its Nominal and Actual Measurements
When dealing with lumber, you need to understand three important terms: Dimensional lumber, Nominal Measurement, and Actual Measurement. Understanding these three terms will help you avoid the usual beginner’s confusion when buying dimensional lumber. Below is a short description of these basic terms when dealing with lumber:
1) Dimensional Lumber
When you shop around for lumber, you will find cut and finished lumber. These cut-and-finished lumber pieces are already planed on all four sides and dried. These lumber pieces usually come in standard sizes and are referred to as dimensional lumber. You will find these lumber pieces in various dimensions like 2x4s, 1x2s, and 2x3s. Besides, you can buy these dimensional lumber pieces at big box home improvement stores and lumberyards.
Wood boards get usually classified according to different metrics, and one classification of wood boards is dimensional lumber. You can purchase dimensional lumber in predetermined sizes, and their sizes are standardized.
A 2×4 lumber, for example, means its thickness is 2″ while its width is 4″. Thus, it gets referred to as 2×4. However, as mentioned above, once you bring home a 2×4 dimensional lumber and measure it using your measuring tool, you will soon discover that its actual dimensions are different from 2 inches by 4 inches. Such a discovery might confuse you and those who don’t understand dimensional lumber.
The nominal size of lumber refers to the board dimensions before they are cured and planed. However, once the lumber undergoes the refinement process, its dimensions become 1.5″ x 3.5″, which gets referred to as the actual dimensions of the refined lumber. In summary, dimensional lumber pieces are those lumber pieces that come in various predetermined dimensions and sizes. They are not rough but have undergone planing on all four sides.
2) Nominal Lumber Sizes
Nominal lumber sizes are the names used to refer to dimensional lumber measurements. The nominal dimensions refer to the board’s dimensions before it undergoes planing and kiln drying. Examples of nominal sizes include 2×4, 1×2, and 1×3.
3) Actual Lumber Sizes
Another term you need to be mindful of is the actual lumber size. The actual lumber size refers to the dimensions of lumber pieces cut to the standard size. It refers to the exact dimensions of the lumber piece after they have been kiln-dried and planed.
Thus, if the dimensional lumber is 2×4, its actual sizes after it underwent refinement are 1-1/2 x 3-1/2 inches. The actual size of the lumber is usually shorter and smaller than the nominal lumber size.
The actual size is usually smaller by one-fourth inch to the three-fourth inch than the nominal dimension of the lumber. As an aspiring woodworker, you can avoid frustration by being familiar with the difference between the nominal and actual lumber sizes.
Why Are the Actual Dimensions of Lumber Smaller than the Nominal Dimensions?
You can buy softwood like fir and pine as dimensional lumber. These pieces of lumber get often used for framing and other woodworking applications. Yet, the reason actual dimensions are smaller than the nominal ones has its historical origin. Long ago, loggers cut 2x4s from green boards with sizes of 2x4s. When these cut board pieces got dried and planed, they ended up smaller.
Over time, however, the standard dried and planed 2×4 dimensions became almost 1-1/2 x 3-1/2 inches. Thus, the standardized sizes of 2x4s actually have 1-1/2″ x 3-1/2″ dimensions. Moreover, the drying and planing processes of the modern day still leave the board almost 1-1/2 by 3-1/2 inches in dimensions.
Yet, the old ways and practices of referring to these boards have lingered on up to the present. Thus, despite being shorter, the dimensional lumber pieces are still referred to nominally as 2x4s, 1x4s, etc.
In the 1870s, lumberyards started using the designations of 2x4s and 2x6s to refer to dimensional lumber. Nevertheless, it was only in the 1920s that the term “dimensional lumber” became popularly used to refer to lumber that got fashioned out in predetermined cuts. Besides, during this period, builders tried to minimize the costs of wood wastage. Thus, they attempted to develop standard grades and sizes for industrial or building timber.
So, the nominal names refer to the sizes of wood before they even get planed or refined. Besides, wood also shrinks as it dries, whether you air-dry or kiln-dry them. Moreover, contemporary sawing, planing, and drying technologies have gone a long way.
Several years ago, however, consumer groups sued some big box stores for false advertisement because they sell undersized lumber pieces. The courts, however, found that there was a distinction between the nominal and actual sizes.
Builders, architects, buyers, engineers, and even sellers are mindful and familiar with these differences. Besides, the courts discovered that calling lumber by their nominal sizes was a long-standing practice.
However, the courts mandated that the use of nominal labels on wood should also indicate the minimum or actual sizes of the wood. Thus, you will now see the nominal and actual sizes of the wood on their labels.
|Actual Sizes||Nominal Sizes|
|1.5” x 3.5”||2×4|
|1.5” x 5.5”||2×6|
|1.5” x 7.5”||2×8|
|1.5” x 9.25”||2×10|
|¾” x 1.25”||1×2|
|¾” x 2.5”||1×3|
|3/4“ x 3.5”||1×4|
Softwood and Hardwood Lumber Sizes
When buying softwood and hardwood lumber, you will notice a difference in their labels. For example, softwoods like spruce, hemlock, and fir show their nominal dimensions, including width and thickness. You will also see some hardwoods with indicated nominal dimensions, including thickness.
You can also buy hardwoods that are surfaced only on one side. Besides, you can find hardwoods surfaced on both sides or two sides. You can also buy hardwood by volume unit referred to as board foot instead of board dimension. Moreover, you can multiply the wood’s nominal width, thickness, and length to calculate the board foot.
Sizing of Hardwood
You will notice that hardwoods get often sized according to the number of their surfaced sides. They also seldom get sold using standard dimensions. Instead, you can get them in quarters or board foot. Besides, the sizing standards for hardwoods like mahogany, birch, maple, and oak become even more complicated when they get used for furniture and cabinetry.
The reason is there are varying measurement standards utilized, notwithstanding the dependence of sizing on whether the boards are surfaced on two sides or one side.
Thus, you can seldom purchase hardwoods in standard dimensions. However, suppliers of hardwoods sell them in board foot or unit of volume. A board foot is 144 cubic inches of lumber, equal to one inch thick with a width of 12 inches.
Furthermore, you can also buy hardwoods in quarters. Every quarter is equal to ¼” thick. This means that a 5/4″ board is 1.25″ thick. So if you need a one-inch-thick board, you might as well buy a 1.25″ board and have it milled down to the correct size.
Sizing of Softwood
When it comes to softwood, you will notice that softwood lumber pieces come in different measurement standards. Besides, there are many factors to consider and be familiar with. It will be best to know the basics of these standard lumber sizes.
You will find softwoods get cut with all four sides finished. They come in standardized sizes. Thus, you will also find softwood lumber used for frames of buildings from where the name dimensional or framing lumber originated.
Dimension lumber may technically mean sawed softwood lumber with thicknesses ranging from two to five inches and widths from four to twelve inches. Besides, dimension lumber ranges in length from six to twenty-four inches.
You can find the standardized sizes of lumber in the American Softwood Lumber Standard. This standard lists the minimum dressed or nominal sizes of nonstructural and structural lumber.
Thus, you can find softwood lumber in sizes ranging from 2×4 to 2×12. However, as mentioned above, the nominal standard sizes are larger than the actual sizes of dimension lumber.
Understanding Board Sizing
If you would buy 1×4 and 1×6 boards, you will notice that their thickness is ¼” less than the nominal dimension and ½” less in width when they leave the mill. Thus, if you’re not mindful of this difference between nominal and actual sizes, you might get confused and even tag your lumber provider for false advertisement. If you buy the larger 1x boards like 1×8 and 1×10, you will notice that they are smaller by ¾”.
If you buy 2x board sizes, like 2x4s and 2x5s, you will notice that they are smaller by half an inch in thickness and width before they leave the mill. Thus, the 2×4 is actually 1.5″ bx 3.5″. On the other hand, the larger 2x wood boards would lose around ¾” in width after refinement, meaning if you buy a 2×10 board, its actual size is 1.5″ by 9.25”.
Having read the abovementioned differences between nominal and actual lumber sizes, you will likely understand why the lumber pieces you purchase are smaller than what they are advertised for. You will also know that lumber production’s long history brings about this size discrepancy. This discrepancy in size is due to a tradition that is hard to do away with. Hence, whenever you have a project, you can now select the correct dimensions of the wood you will be buying for your projects.
It may seem preposterous that in our times when standardization is already the norm of the day, we still find that dimension lumber has not been strictly standardized. Nevertheless, the good thing is that whoever you are, whether you are an engineer, contractor, or woodworker, the lumber pieces you are buying are almost the same in size anywhere in the country.
Liam is a 37-year-old woodworker and interior designer who loves to make every furniture project an art piece. He is very experienced in furniture design and woodworking project planning.