What is 8/4 Lumber? Wood Thickness + More Explained

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Are you embarking on a woodworking project that requires 8/4 lumber, but find yourself grappling with questions about what it entails, how to gauge its dimensions, and its typical availability? 

Allow me to demystify the world of 8/4 lumber and equip you with comprehensive knowledge to empower your next woodworking endeavor. Let’s unveil the intricacies of 8/4 lumber and related insights, ensuring you’re well-prepared for your upcoming project.

What is the Thickness of 8/4 Lumber?

8/4 lumber is a nominal measurement of 2 inches thick. Once the rough-cut lumber comes out of the sawmill, it is 2 inches or eight quarters of an inch thick. After the planing process, it will be down to 1 and ¾ inches.

milling 8/4 lumber

The optimal orientation for lumber in certain applications, such as when placing it on the floor or a bench, is to have it “set on edge.” This means that the lumber should rest on its long, narrow edge.

Now, if you’re considering crafting a benchtop, a key technique is to glue the broader sides of the boards together to create the top surface. This approach not only enhances stability but also ensures a smooth and resilient work surface for your bench. 

It’s a tried-and-true method that most experts strongly recommend for achieving the best results in your woodworking projects.

Why is it Measured This Way?

Lumber mills use the quarters sizing method to measure the dimensions of a rough sawn lumber. It refers to the thickness of the lumber as lengths and widths differ depending on what type of log the wood is from. 

Generally, a lumberjack will plane the woods to the necessary thickness. They will rip and glue them together to reach the desired width. Rough cut lumber has “true” thickness reflected by the quarter sizing method. 

milled lumber

According to the sizing method, an inch of lumber reflects how many quarters it has. The National Hardwood Lumber Association [1] created the quarter sizing system back in 1898. They aim to promote a uniform system not to confuse the woodworkers and customers. 

It also makes their quality checking and inspection job easier.

Interesting Read

Pricing in Relation to Lumber Thickness

The price of the lumber depends on how thick it is. It also depends on the number of woods you are going to purchase or whether there is a scarcity of the lumber you wish to purchase. I have made lumber calculation easier in one of the other articles but look at the example below to give you an idea.


To get the size of the board feet, multiply the length in feet by the width and thickness in inches. Divide the answer by 12.  For example, I have 10 ft x 8 in x 4 in / 12. The board feet will be equal to 26.67. You can now multiply 26.67 by the total number of board feet you need.

Lastly, you can multiply the answer to the price per piece of the board foot again to get the total cost.

Correct Thickness of Different 8/4 Lumber

Green or Air-Dried

For green, freshly sawn lumber, the inspection area should have a thickness of 2 inches for 8/4 lumber. However, keep in mind that this size will shrink as it goes from green to air-dry. It’s important to note that the shrinkage may vary between different types of lumber.

air drying lumber

Additionally, if you are using a quartersawn, the shrinkage will be double compared to a flatsawn. A reasonable estimate is about 3 percent in thickness as it goes from green to air-dry. The thickness is not an issue if the lumber is not graded after air drying.

Kiln-Dried Rough

The NHLA has a kiln-dried rule. The rule applies to the grading process of the rough kiln-dried lumber. For 8/4 lumber, the thinnest spot should be ⅛ inch and a minimum thickness of 1 ⅞ inch in the grading area. 

stacking lumber from the mill

Some companies allow up to 3/16 inches to make sure that it is not going to shrink too much during the drying process.

Kiln-Dried Planed

Lastly, kiln-dried lumber is surfaced on two sides or planed before grading. In this process, the dimension of the lumber is given enough allowance so that they can keep its size closer to 2 inches. 

Unplaned and cheaper hardwoods are graded on the poor side. In contrast, planed lumber is graded on the better side. For 8/4 lumber, planing can take off as much as one inch.

How to Find 8/4 Lumber Near Me

You can find an 8/4 lumber near you by typing in your place and the lumber size you need in Google. Filter each wood source to ensure that you can get the best lumber for your workbench top project. 

If they have a physical store, that is much better because you can check the lumber yourself.


Now that you’re acquainted with the concept of 8/4 lumber, you’re in a better position to make precise calculations for your wood requirements. Furthermore, you’ll be equipped with valuable insights into estimating the overall cost of your project. 

The need to perform on-the-fly measurements in the store to avoid any intimidation will be a thing of the past. Feel confident in your woodworking endeavors with this newfound knowledge!

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Robert Johnson is a passionate furniture maker & carpenter, sought after for his knowledge on the craft.
You’ve probably seen his down-to-earth wisdom in USA Today, Bobvila, Family Handyman, and The Spruce, where he has shared commentary and guidance on various woodworking topics.

Robert is the brain behind Sawinery, where he aims to share tips, tricks, and a passion for all things carpentry.

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