If you don’t buy hardwood lumber every day, terms like 4/4, 5/4, 6/4 and 8/4 can be confusing.
What does 4/4 mean? How do you pronounce it? Is 8/4 actually two inches thick?
These are common questions we hear from customers, and fortunately, the system is pretty simple once you understand it.
Hardwood lumber is traditionally sold in thicknesses measured in quarters of an inch. The easiest way to understand the system is to think of the number as fractions of an inch…
4/4 = four quarters = 1 inch
5/4 = five quarters = 1-1/4 inches
6/4 = six quarters = 1-1/2 inches
8/4 = eight quarters = 2 inches
Here’s a quick reference:
|
Lumber Thickness
|
Rough Thickness
|
|---|---|
|
4/4
|
1″
|
|
5/4
|
1-1/4″
|
|
6/4
|
1-1/2″
|
|
8/4
|
2″
|
|
10/4
|
2-1/2″
|
|
12/4
|
3″
|
|
16/4
|
4″
|
So, when you see Wood Vendors offering Walnut, White Oak or another hardwood in different quarter thicknesses, you’re choosing the starting thickness of the lumber.
How Do You Pronounce 4/4 Lumber?
You don’t normally say “four-fourths.”
In the hardwood lumber industry, 4/4 is pronounced “four-quarter.”
Likewise:
- 5/4 = “five-quarter”
- 6/4 = “six-quarter”
- 8/4 = “eight-quarter”
- 10/4 = “ten-quarter”
- 12/4 = “twelve-quarter”
- 16/4 = “sixteen-quarter”
For example, if you’re calling us looking for Walnut, you might say:
“I’m looking for about 200 board feet of eight-quarter Walnut.”
When Would You Use 4/4 Lumber?
4/4 is one of the most common hardwood lumber thicknesses.
It’s a good starting point for many projects, including:
- Cabinets
- Furniture components
- Shelves
- Trim
- Panels
- Mouldings
- Millwork
A typical clean-up thickness for 4/4 lumber is around 13/16″, meaning the faces have been surfaced smooth with no skip. That makes 4/4 a common starting thickness when the finished part needs to be approximately 3/4″ thick.
When Would You Use 8/4 Lumber?
8/4 is much thicker stock, giving you considerably more material to work with.
Common uses include:
- Table legs
- Furniture legs and posts
- Thick tabletops
- Benches
- Mantels
- Heavy millwork
- Turning
- Larger architectural components
For example, if you’re making a table leg that needs to finish at 1-1/2″ square, 4/4 stock isn’t thick enough. You would need to start with thicker lumber, such as 8/4.
Here’s the Important Part: 4/4 Doesn’t Necessarily Measure 1″
This is where the quarter system can cause confusion.
4/4 describes the starting thickness of the rough lumber. It does not mean a surfaced board will measure a full 1″ thick.
Think about a rough-sawn board. Its faces aren’t perfectly smooth and flat. To produce a clean, flat surface, material has to be removed.
That means a 4/4 board will become thinner as it is surfaced.
So, if your project absolutely requires a finished piece that is a full 1″ thick, don’t automatically order 4/4 and assume you’ll get there.
You’ll need to start with thicker material, such as 5/4 or another appropriate thickness.
Start With Your Finished Thickness
When deciding whether you need 4/4, 5/4, 6/4, 8/4 or something thicker, the best question to ask is:
What thickness does my finished piece need to be?
If you need approximately 3/4″ finished material, 4/4 may be a good starting point.
If you need a full 1″, you’ll need thicker stock.
And if you’re making substantial furniture legs, posts or other thick components, you may need 8/4 or thicker material.
Tell us the species, what you’re building and the finished thickness you need. We’ll help you work backward from there
We can help you determine the appropriate starting thickness for your project.
Next in our Understanding Lumber series: Learn the difference between nominal and net lumber dimensions and why the size lumber is called isn’t always the size it actually measures.