What is 5/4 Lumber? What does 5/4 Lumber Mean?

What is 5/4 Lumber? What does 5/4 Mean? And how do you say it?

If you are doing a home improvement or craft project, you may find yourself purchasing some lumber, either softwood or hardwood. While browsing the options, you may notice that the dimensions wood is sold by are often not the actual dimensions of the boards. 

Wood is sold by nominal measurements, not actual measurements. Plus, hardwoods and softwoods have different standards. All of this can make it a little bit confusing when you are trying to make a purchase! 

A common question newer woodworkers or DIY-ers may have is “what is 5/4 lumber?” While it may appear that it is a fraction of how thick the lumber may be, it isn’t exactly a direct measurement. 

5/4ths is a common pre-cut of lumber, but the actual thickness of the board is 1.25 inches.

The Actual Size of 5/4 Lumber

While softwoods are sold in more standard dimensions, hardwoods rarely are. Supplies tend to sell hardwoods by board foot instead (which is a volume unit.) A board foot is roughly equivalent to 144 cubic inches. However, hardwoods can also be sold in quarters, and ¼ inch of thickness is equivalent to one quarter.

Following these rules, a 5/4 board is 1¼ inches thick. 

Pro Tip: The thickness of a hardwood board is measured before surfacing! You will need to account for this when working on your project because you will lose a little thickness after planing. When it comes to 5/4 lumber, you will usually end up with a finished board that is 1.063″ thick.

Understanding the Quarter System

This system may seem confusing, but if you look at it a little more closely, it becomes easier to understand. Quarters refer to the thickness of rough-sawn lumber measured in ¼-inch increments. 

Instead of reading it as a fraction, it should be read as a number of quarters: 5/4 is five quarters, 4/4 is four quarters, etc. Just as the 5/4 board is 1¼-inches thick because it is five quarters, a 4/4 board is 1 inch thick because it is four quarters. A 12/4 board would be three inches thick…and so on and so on. 

Keep in mind, quarters are generally only used to measure the rough stock. Once the boards are surfaced, people generally use actual thickness measurements. If your board was 6/4 when it was rough, you would refer to it as 1½-inch after surfacing. (Assuming you lost the standard ¼-inch of material during surfacing.) 

The quarter system is generally the “jargon” that you will hear in professional spaces. You will most likely find that a lumber supplier will use the quarter system, but there may be a more simple system in place at a big box home center.

What is 5/4 Lumber Used For

Hardwoods can be used for a multitude of projects. Things like boats, furniture, musical instruments, and home flooring are all made from hardwoods due to their durability and appearance. Plus, different hardwood species may lend themselves to particular projects. 

When it comes to 5/4 boards, one of the most popular projects is decking. In North America, a vast majority of decks are built with 5/4 boards. This is because it is generally an economical choice that is easy to work with. Plus, many people like that it can be an eco-friendly choice. For instance, if two similar-sized decks are made, one with 5/4 boards and one with 2×6 boards, the 5/4 board deck will require fewer trees to be cut down to get the same amount of wood. 

When it comes to a deck, you have to consider the elements, things like moisture and insects can wreak havoc! That is why people tend to use specific types of wood for these projects. One of the most common hardwood deck building materials is 5/4 boards of mahogany. This hardwood is very durable and is naturally resistant to warping and damage caused by insects. While it may be a more expensive choice initially, the deck is likely to last for several decades.

How do you Say 5/4 Lumber? What do you call 5/4 Lumber?

how do you say 5/4 lumber

But how do you say it? 5/4 lumber is called a few different terms.  The term can vary regionally, or by profession, as some trades will use different terminology depending on what works for them. However, here’s two that you can’t go wrong with:

How to say 5/4 Lumber:

  • “Five-Fourths” Lumber
  • “Five-Quarters” Lumber

Both are just as correct as the other, and if you were to use one term around someone who uses another term, they would still know what you’re talking about. After all, it only wood, not space hieroglyphs.

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