What is 4/4 Lumber? Wood Thickness + More Explained

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Generally speaking, lumber is sized according to its thickness. There are 4/4, 5/4, 6/4, 8/4, and 12/4 sizes. But the most commonly used is the 4/4. Knowing what lumber you need to use is crucial as it affects the overall structure of your wood project. Here we’ll discuss more what 4/4 lumber is, its size, and properties. 

What Does 4/4 in Lumber Sizes Mean?

In terms of lumber sizes, 4/4 is short for “four quarters of an inch.” If you’re sharp with numbers, 4/4 is about 1 inch. To better understand the sizing, refer to the following: 

lumber sizes

One way to determine the actual thickness of a piece of lumber is by referring to the stage it’s in, referred to as RGH or S2S. While both terms refer to the rough or surfaced part of the lumber, all types start out rough.

What Do These Fraction Sizes Mean?

These fraction sizes tell you how thick the lumber is. It’s more than just a name and an exact lumber measurement. Some factors incorporate into it. We see sizes like 2×2 and 4×4, but it’s not 2 inches by 2 inches and 4 inches by 4 inches. In woodworking, it has a different approach. There comes nominal lumber and dimensional lumber.

How Thick is 4/4 Lumber?

The 4/4 lumber has a thickness of about 1 inch. Our experts noted that the “quarter system” is commonly used when referring to thickness in the hardwood lumber industry.

one inch thick lumber

How Wide is 4/4 Lumber?

Hardwood lumbers are typically sold in random widths, regardless of their thickness. There are local lumberyards that sell 4/4 lumbers in dimensional widths like softwoods. 

More About the 4/4: The Most Common Lumber Size

Comparing Rough Sawn and Surfaced Lumber

One of the biggest differences between rough sawn and surfaced lumber is the weight. Also, it’s commonly believed that rough lumber is cheaper than its surface counterpart. 

While the price difference is significant, the weight difference between surfaced and rough sawn is also important when it comes to transporting containers and loads. 

A flatbed truck can haul 45,000 lbs of lumber. If the load is surfaced or rough, the cost of moving it doesn’t change. However, the size of the lumber that the truck can fit changes. You can fit about 11,000 board feet of rough sawn. But, with surfaced lumber, you can fit 14,000 board feet onto the truck. 

different lumber sizes

In general, it’s better to pay the wholesale distributor the marginal fee instead of the usual flat fee for surfacing. This will allow you to fit more lumber on your container or truck.

Rough Sawn



Surfaced Lumber



Correct Thickness of Different 4/4 Lumber

Green or Air-Dried

According to our pro woodworkers, green lumber will shrink in thickness by around 3 percent when air-dried. For instance, if a smart sawmill is going to cut a 4/4 thick piece of lumber, it should be sawn at a thickness of around 1/32 inch to avoid getting thin after air-drying. 

air drying lumbers

Kiln-Dried Rough

The NHLA [1] has a rule that applies to kiln-dried rough lumber, which allows the thinnest part of the lumber to be 1/16 inch thinner. This rule applies to various grades of lumber, such as 4/4, 5/4, 6/4, 7/4, and 8/4.

Kiln-Dried Planed

When preparing kiln-dried lumber, it is surface-mounted or planed on two sides before it is subjected to grading. An allowance is given for this process. The thickness of the surface is typically as thin as 13/16 inches.

Which is More Preferable: 4/4 or 5/4 Lumber?

The standard way is to use 4/4 lumber. But, sometimes, some shorts of 5/4 lumber is used to get the desired grain type in a certain area. It will really depend on your woodworking needs. If you opt for the standard lumber size, then 4/4 is preferable.  

Also Read: Actual Size of 2×8 Boards


Woodworking may be confusing, especially if you’re new to this field. But, having some basic info about the SXS lumber designations, what 4/4 lumber and other sizes means is valuable knowledge you can apply as you go through the woodworking industry. There’s so much more to learn, and you should begin now!

Robert Johnson is a woodworker who takes joy in sharing his passion for creating to the rest of the world. His brainchild, Sawinery, allowed him to do so as well as connect with other craftsmen. He has since built an enviable workshop for himself and an equally impressive online accomplishment: an extensive resource site serving old timers and novices alike.
Robert Johnson
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