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Here's the simple truth: 4/4 lumber (You'll hear it called "four-quarter") is the hardwood lumber industry's way of saying a hardwood board is rough-sawn to one inch thick. It's the standard starting point used by sawmills and suppliers before the wood gets smoothed down, making it the foundation for countless woodworking projects.
When you step into a lumberyard or shop for hardwoods online, you’ll notice they aren’t sold like the pine 2x4s from the big-box stores. Instead, hardwoods use a "quarter system," which is just a straightforward way to talk about the thickness of rough-sawn wood in quarter-inch steps.
So, when you see 4/4, it literally means four quarters of an inch—which, of course, simplifies to one full inch.
This system is crucial because a board’s thickness changes as it goes from a raw slab to a finished product. A rough-cut board straight off the sawmill is thicker and has a coarse, fuzzy surface. To get it ready for a project, it needs to be planed smooth, and that process shaves off material. The 4/4 name tells you its original thickness before any of that happens.
If there's one thing every woodworker needs to get right, it's the difference between nominal and actual thickness. Think of the nominal size as the name—in this case, 4/4 or one inch. The actual size is what your tape measure will read after the board has been surfaced smooth.
Key Takeaway: A 4/4 board is only one inch thick when it's rough and unfinished. Once it’s planed smooth (surfaced), its final "actual" thickness will be less, typically landing somewhere between 3/4" and 7/8".
This is a necessary step to prepare the wood. Surfacing creates flat, parallel faces, making the board stable and ready for joinery. Understanding this difference saves you from the headache of buying wood that’s too thin for your project.
To make it crystal clear, here’s a quick breakdown of how the quarter system translates to real-world measurements for both rough and surfaced lumber.
| Quarter System Name | Nominal Thickness (Rough) | Typical Surfaced Thickness (S2S/S4S) |
|---|---|---|
| 4/4 | 1" (25.4 mm) | 7/8" to 3/4" (19-22.2 mm) |
| 5/4 | 1.25" (31.75 mm) | 1" to 1-1/16" (25.4-27 mm) |
| 8/4 | 2" (50.8 mm) | 1-3/4" to 1-13/16" (44.5-46 mm) |
This distinction is what ensures you always walk away with the right material for the job.
Now that you know what to look for, exploring a curated collection is a great next step. You can see a wide variety of species in our selection of 4/4 lumber to find the perfect match for your design.
Walk into any real lumberyard, and you'll hear terms like 4/4, 5/4, or 8/4 thrown around. At first, it feels like you're trying to crack a secret code. But this "code" is actually a brilliantly simple system that sawmills have used for generations to create a universal language for hardwood thickness. It’s called the quarter system, and it’s the backbone of how hardwood is sold.
The logic behind it is surprisingly straightforward. The system measures the thickness of rough-sawn lumber in quarter-inch increments. The first number in that fraction simply tells you how many quarter-inches thick the board is.
Think of it like stacking coins. If one quarter equals a 1/4" increment, then:
This standardized approach ensures that a sawmill in one province and a woodworker in another are speaking the same language. Everyone agrees on the starting thickness of a rough board before any finishing work even begins.
So, why the heck don't we just label a board "1-inch thick" and call it a day? The answer is all about the journey wood takes from the mill to your workshop. The quarter system refers specifically to the nominal thickness—the measurement taken right after the log is sawn, while the wood is still rough and green.
As you learned earlier, this rough board is almost never its final dimension. It has to be dried, then surfaced (planed smooth) to become flat, stable, and ready for a project. Every one of those steps shaves off a little bit of material.
By using the quarter system, the industry establishes a clear, consistent starting point. It tells you the full amount of material you begin with, letting you plan for the final, slightly thinner dimension you'll have after milling.
For example, a furniture maker who needs a final finished thickness of at least 7/8" knows they have to start with 5/4 lumber. Why? Because 4/4 stock (which finishes around 3/4") simply won’t be thick enough after it’s been flattened and smoothed.
Understanding the "why" behind the system empowers you to choose the right raw material every single time. It prevents costly mistakes and ensures your project dimensions are spot-on from the start, turning a confusing fraction into a practical and indispensable planning tool.
If there's one concept that trips up new woodworkers more than any other, it's this. Getting it wrong can derail a project before it even starts. The thickness you see on the price tag, like 4/4, isn't always the thickness you'll measure with your calipers. Understanding the difference between nominal and actual thickness is absolutely essential for buying the right material.
Think of it like this: Nominal thickness is the board's name—its starting point. It refers to the dimension of the lumber when it was first rough-sawn at the mill. For 4/4 lumber, this is one full inch. But this rough board has a coarse, uneven surface that's no good for fine woodworking.
To become usable, that board has to be milled flat and smooth. This process, known as surfacing, involves sending it through jointers and planers, which shaves off wood to create perfectly parallel faces. The final, smooth dimension you’re left with is the actual thickness.
The amount of wood removed depends entirely on how finished the board is when you buy it. Lumber is sold in a few different states, each impacting its final thickness:
Ignoring the gap between nominal and actual can be a costly mistake. Let's say your project plans call for a finished tabletop that's exactly 7/8" thick. If you buy 4/4 S4S lumber, which only measures 3/4", you’re already out of luck. You simply don't have enough material. To hit that target, you would have needed to start with thicker 5/4 stock.
The Golden Rule: Always, always plan your project around the actual thickness of the lumber you’re buying. Before you purchase, confirm with your supplier whether their stock is rough, S2S, or S4S. This way, you know precisely what dimensions will land in your workshop.
Getting this right from the start prevents frustration, saves money, and ensures you buy the correct amount of wood for the job.
To help you plan, here's a quick cheat sheet for some of the most common hardwood thicknesses you'll encounter.
| Nominal Thickness | Imperial (inches) | Metric (mm) | Typical Surfaced Actual Thickness (Imperial) | Typical Surfaced Actual Thickness (Metric) |
|---|---|---|---|---|
| 4/4 | 1" | 25.4mm | 3/4" to 7/8" | 19mm-22.2mm |
| 5/4 | 1.25" | 31.75mm | 1" to 1-1/16" | 25.4mm to 27mm |
| 6/4 | 1.5" | 38.1mm | 1-1/4" to 1-5/16" | 31.75mm to 33.3mm |
| 8/4 | 2" | 50.8mm | 1-3/4" to 1-13/16" | 44.5mm to 46mm |
| 12/4 | 3" | 76.2mm | 2-3/4" to 2-13/16" | 69.8mm to 71.4mm |
Keep this chart handy. Knowing these numbers will make you a much smarter lumber buyer and help ensure your projects turn out exactly as you envisioned.
Now that you've got a handle on what 4/4 lumber actually is, we get to the fun part—putting it to work. This versatile thickness is arguably the most common choice for a massive range of woodworking projects, and for good reason. Its final dressed 4 sides thickness of around 3/4" hits the perfect sweet spot between strength, stability, and workability, making it the go-to for countless builds.
Think about a set of custom kitchen cabinets. The doors and drawer fronts need to feel solid and durable, but not clunky. This is exactly where 4/4 lumber shines. It's got enough backbone to stay flat and resist warping over time, all while looking elegant and well-proportioned.
This material's perfect balance makes it ideal for projects where good looks and solid construction are equally important. You'll find it’s the perfect starting point for creating beautiful pieces that are built to last.
Some classic uses include:
The common thread here? 4/4 gives you enough substance for strength without adding unnecessary weight or bulk.
Why It Works: A finished 4/4 board is thick enough to handle all kinds of joinery—from simple dowels to more complex mortise and tenons—giving you the flexibility to build strong, long-lasting connections.
As much of a workhorse as 4/4 is, it isn't the right choice for every single job. Knowing its limits is just as important as knowing its strengths. The key is to think about the structural load and the visual weight your project needs.
For instance, if you were building a big dining room table, you'd almost certainly want thicker material. You just can't get chunky, two-inch-thick table tops out of 4/4 stock.
This is where thicker lumber comes into play:
Choosing the right stock is all about matching the material to the task. If you start with 4/4 lumber for your general-purpose projects and only size up when the design demands it, you can plan your builds with confidence and efficiency.
Walking into a lumberyard packed with towering stacks of wood can feel a little overwhelming. But if you know what you're looking for, you can confidently pick out the perfect 4/4 lumber for your project and get the best bang for your buck. It all comes down to understanding a few key trade-offs before you start sorting through the pile.
The first big choice you'll face is between rough sawn and surfaced lumber. Rough sawn boards come straight from the mill and are cheaper, but they demand a jointer and planer to flatten them out. Surfaced lumber (like S2S or S4S) is ready to go right out of the gate but costs more because of that extra milling. Your decision really hinges on your budget, what tools you have in your shop, and how much prep work you’re willing to put in.
Unlike the simple per-board price you see at big-box stores, hardwoods are almost always sold by the board foot. This isn't a measure of length; it's a measure of volume. Think of one board foot as a slab of wood that's 12 inches long, 12 inches wide, and one inch thick.
Trying to calculate this in your head can be a bit tricky, but it's crucial for figuring out your project's budget. The formula looks like this:
Here's the quirky part: for 4/4 lumber, the thickness is always counted as 1 inch in this formula, even if the board has been planed down to 7/8". It’s a bit of a head-scratcher at first, but our comprehensive guide explains in detail what a board foot is and how to master the math.
Buyer's Tip: When you're buying rough lumber, you'll often find it sold as "random widths and lengths" (RWL). This just means the boards in a stack won't be uniform. Be ready to dig through the pile to find the specific dimensions you need for your project.
Beyond the price tag and the dimensions, a few other quality checks will ensure you bring home great material. Always give the boards a once-over for these three things before you head to the checkout:
Keep these points in mind, and you'll be selecting top-notch 4/4 lumber with the confidence of a seasoned pro.
To wrap things up, let's tackle some of the most common questions woodworkers have about 4/4 lumber. Consider this your quick-reference guide for clearing up any lingering confusion and making sure you’re confident the next time you’re buying hardwood.
In its rough-sawn state, right off the sawmill, 4/4 lumber is nominally 1 inch thick. But that’s just the starting point, not the finished dimension you'll be working with.
Once it's been surfaced smooth on two faces (S2S), its actual thickness usually lands around 13/16 of an inch. If you buy it surfaced on all four sides (S4S) and ready for your project, it’s typically closer to 3/4 of an inch thick. It's always a good idea to double-check the final dimensions with your supplier, as milling practices can vary a little.
No, and this is a really important distinction. A "1x" board you'd find at a big-box store (like a 1x6) is almost always a softwood like pine or fir. It's already been surfaced down to its final dimension of 3/4 of an inch thick.
On the other hand, the term 4/4 belongs to the hardwood quarter-thickness system. A 4/4 board starts at 1 inch rough and is sold either in that state or surfaced to around 13/16". The grading, species, and applications are completely different—4/4 is the standard for fine furniture and cabinetry, not general construction.
Quick Comparison: Think of "1x" boards as the stuff you build a deck or frame a wall with. "4/4" lumber is what you use to build a beautiful piece of furniture. Their names might sound similar, but their purpose and material are worlds apart.
Absolutely. 4/4 lumber is an excellent choice for many kinds of tabletops, especially for smaller pieces like end tables, coffee tables, or desks where you don't need a super thick, heavy look. Its finished thickness strikes a great balance between elegance and strength.
For bigger dining tables, some builders prefer the of 8/4 or 10/4 stock. That said, a well-built tabletop made from high-quality 4/4 hardwood with a stability element such as a skirt will be beautiful, strong, and more than durable enough for daily use.
The quarter system is really just a standardized language for the entire hardwood industry. It gives sawmills, suppliers, and woodworkers like us a consistent way to talk about the thickness of rough-sawn lumber before it gets dried and milled.
Since the final thickness changes depending on how much material is removed during surfacing, starting with a reliable nominal measurement (like 4/4, 5/4, or 8/4) creates a universal baseline. It all comes back to that initial sawn thickness at the mill, which is the most important measurement when you're sourcing raw material.
At The Knotty Lumber Co., we make it easy to find the perfect 4/4 lumber for your next build, with high-quality hardwoods ready to become your next masterpiece. Browse our complete collection of domestic and exotic hardwoods today!
