What’s the difference between Lumber Nominal and Actual size ?

The lumber size is one of the biggest catches when purchased, you will find that the timber advertised size is not the product’s actual size.

This is a big deal, identifying the nominal and real sizes are a good skill. Trust me, and this will be achievable in this article.

However, it would be best if you understood some of the most used lumber species, with most standards, lumbers sources which are: 

  • Redwood 
  • Pine 
  • Cedar 
  • Maple 
  • Cherry

Identifying the best lumber

Almost all homeowners will work with lumbers at the primary stage of their project. You may be experiencing uncertainty regarding the actual or nominal size of a wood product. To solve this puzzle, it is essential to:

  • look at the thickness, 
  • look at the width, 
  • and look at the length of the board when purchasing wood, 

Whether hardwood or softwood, to decide what would fit any application.

The wood’s length rises typically by 2 feet, starting at 8 feet and running 24 feet. The board length is always within 1⁄4″ of the desired size an eighth-foot surface.

Thus, the length is never the issue when talking about nominal and actual board sizes. The thickness and width are the sticking points. For this post, we will concentrate our attention on this.

Dimensional Wood

Dimensional wood is wood that is cut to regular pre-defined sizes. Dimensional wood sizes apply not to length but depth and width. The dimensional wood is sawn, designed, and often thinned to be ready for many applications immediately.

Size wood is the most common type of wood used for construction, as its uniform size enables building manufacturers to use it interchangeably in exclusive use. 

Lumber Nominal Size VS Actual Size

Nominal Size (inches)Actual Size (inches)
1 x 43/4 x 3 1/2 
1 x 63/4 x 5 1/2 
1 x 83/4 x 7 1/4
1 x 103/4 x 9 1/4
2 x 41 1/2 x 3 1/2 
2 x 61 1/2 x 5 1/2 
2 x 81 1/2 x 7 1/4
2 x 101 1/2 x 9 1/4
2 x 12 1 1/2 x 11 1/4
4 x 4 (Post)3 1/2 x 3 1/2
4 x 6 (Post)3 1/2 x 5 1/2
4 x 8 (Post)3 1/2 x 7 1/4
6 x 6 (Post)5 1/2 x 5 1/2
8 x 8 (Post)7 1/4 x 7 1/4

Characteristics of Lumbers

  • The nominal dimension of a piece of wood is usually what the supplier refers to as softwood board is sold in a retail store. 
  • The little and actual width and thickness sizes are “2 by6” and 1-1/2 by 5-1/2, respectively.
  • The nominal size corresponds to the board’s original condition before secondary processing. 
  • These little processes are the drying of the rough-sawn boards’ oven and surface from the “green” scenery. 
  • These secondary processes reduce thickness and width to achieve uniformity to the customer by shrinking or surfacing.

Before Buying lumber

The most crucial explanation for knowing the difference between the real and the nominal dimensions is that you communicate correctly with your wood supplier because:

  • If you buy an actual size 2 1/2″ x 3 1⁄2 in a store, expect a 2 1/2″ x 3 1⁄4 inch. 
  • If your project needs the actual size of the parts 2″ x 4,” may use a different size material in place and build your project based on the existing standard sizes. 
  • If you specialized in ordering dimensional lumber, make sure you communicate the finished product you need with the lumber at a period.

Factors Affecting Sizes of Lumber

Many factors are responsible for differences in lumbers’ sizes between nominal and actual lumber, but let’s consider the three most important factors.


Every greenwood has a higher humidity content. The measurements and sizes decrease as the wood dries, whether through artificial or natural methods. Shrinkage can vary from 2 to 15 percent, depending on the wood species, especially the wood grain direction. Which may help lead to a reduction in actual size.

Ground Surface 

Ground surface refers to dress boards with smooth sides. The smoothing of board surfaces decreases the original width or thickness further. This wood is generally referred to as the S4S name stands for four sides of the body.

Wood type 

Wood species and type is another factor determining the lumber size. 


Before going too much further, I must first confirm that the material in question is indeed a solid wood piece and not a human-made composite or plastic made to resemble wood. 

  • Check The Type Of Lumber

There are different types of wood species, and their lumber bye product differs, such as oak or mahogany, with a pore structure. To achieve this, check the lumber texture. 

  • Check Lumber’s Weight

When having lumber, feel its weight if possible, and compare it to other recognized wood species. Try to reach the edge to make your fingernail feel hard. If you have a scale, the length, width, and thickness of the wood can be measured and combined to calculate the wood density. 

  • Consider The Wood Review

When we try to classify wood, we neglect common sense and reasoning and people’s suggestions. Listen to what people talk about the lumber and wood.

  • Examine the Lumber

Perhaps no other technology to classify wood accurately is as helpful and definitive as a magnified inspection. It also results in a predictable, repeatable, and effective method for the identification process from a largely intuitive, non-scientific process.

  • Look at the color.

Color is the best characteristic of lumber, and every species varies in color, a full color. If the color is even unnatural, the chances are more significant than the whole attempt to distinguish the wood is in vain. 

  • Consider Some Other factors. 

At a particular period, everyone has in mind the best lumber size suitable for a specific job, with personal factors and considering.

In these cases, except when you are left with the only option, specialized and other narrower means of identifying lumber may often be helpful.