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

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Does your project need an 8/4 lumber, and you have little to no idea what it is, how to measure it, and how much it usually is? Our experts will help you understand what 8/4 lumber is and all other related info that will be helpful for your next woodworking project. Read on. 

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

Our experts explained that the orientation of the lumber should be “set on edge,” especially if you’re placing it on the floor or the bench. The lumber should rest on its long narrow edge. If you plan to make a benchtop, you should glue the broader side of the board together to make the top part.

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. Our researchers made lumber calculation easier in one of our 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, we 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

A green, freshly sawn, and cut lumber, the thickness in the inspection area should be 2 inches of 8/4 lumber. However, this size will shrink as it goes from green to air-dry. The shrinkage cannot be the same from one lumber to another.

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

Our team suggests that you 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 know what 8/4 lumber is, you can correctly measure the number of wood you need. Additionally, you can also have an idea about the project’s total cost. You don’t have to be intimidated and calculate the size in the store if needed. 

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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