2×4 Actual Size: Simple Answer + Facts
One of the most commonly used woods is the classic 2×4, since its dimensions make it ideal for a variety of construction and woodworking projects.
But is a 2×4 actually 2″x4″? The short answer is no, but why?
In this post, I’ll discuss everything you need to know about the actual size of a 2×4, including why there’s a size discrepancy in the first place.
- 2×4 boards are really 1.5″x3.5″, meaning they’re 1.5″ thick and 3.5″ wide. In meters, 2x4s are actually 38mm x 90mm.
- 2x4s can vary in length (span), but most are 8′ long.
In This Article:
Actual Size of a 2×4
The actual size of a standard 2×4 is 1.5″x3.5″.
Therefore, when you’re planning a construction project that involves several 2x4s, you need to make sure you use the actual dimensions and not the dimensions that are commonly used to describe these boards, i.e. 2″x4″.
It’s possible to find boards with an actual size of 2″x4″, but these aren’t 2″x4″ when first cut so they can’t be classified as 2x4s.
Actual Size of a 2×4 in MM
A standard 2×4 is 38mm x 90mm, so if you see these dimensions on a board you know you’re looking at something that’s really 1.5”x3.5”.
What Is Dimensional Sizing?
Dimensional sizing is the most commonly used measuring system for wood and wood-based materials.
If you go to any big-box hardware store that sells wood, the vast majority of the wood you’ll encounter is measured using dimensional sizing.
When I say dimensional sizing, I’m referring to the measurement calculation: width x thickness.
Many people see the #x# calculation and naturally think it’s length x width, but this isn’t the case. In fact, 2x4s can vary in terms of length, and the same is true of 2x6s, 4x4s, etc.
But despite being called 2x4s, these boards are not 2”x4”, rather they’re 1.5”x3.5”.
When a board is first cut, it is 2”x4”, but the drying process and a couple other factors reduce its size to 1.5”x3.5”.
Dimensional Lumber: Nominal Size vs. Actual Size
When it comes to dimensional lumber, the term “nominal size” refers to the lumber’s size before it’s dried, machined, and prepped for sale.
A 2×4’s nominal size is 2”x4”, meaning it’s this size before processing.
Actual size, on the other hand, refers to the lumber’s actual dimensions.
In the case of a common board 2×4, the actual dimensions are 1.5”x3.5”.
A few reasons explain why both nominal and actual dimensions are used to indicate wood’s size, and these are discussed in detail in the section below.
Why is a 2×4 not 2″ by 4″?
There are a few key reasons why 2x4s aren’t actually 2”x4”, and all but one have to do with material scarcity in some way.
In the United States specifically, mass production of lumber and wood began in the early 1870s.
Back then, wood was cut to order, so sizes always varied. Still, the ultimate size of a board was determined by the builder on site, which is still how it is nowadays.
During the early years of American wood mass production, people viewed timber as an unlimited resource, one that was readily available for construction and other purposes.
But as U.S. growth picked up, so did the demand for new constructions, and wood was needed more than ever before.
At the time, most US-grown timber came from forests around, Boston, New York, Philadelphia, and Baltimore, mainly because these cities were major transportation hubs.
Eventually, it became clear that these forests were being over-harvested, which led to cities like Chicago, Albany, and Bangor taking the reins as the country’s main wood suppliers.
At a certain point, there was extreme demand for wood that grew in southern pine forests, like longleaf pine, loblolly pine, and slash pine. Such forests are known as pineries.
In addition to Southern yellow pine, there was also demand for western Douglas fir, western hemlock, and the many species that are commonly found in spruce forests.
Early in the 1900s, demand for “common lumber” was significant across the lumber industry, and eventually retail lumberyards got together and pushed for more regulation of wood measurements and standards.
In 1919, the first American Lumber Congress called for uniformed sizing, but nothing came of it since there was a lot of disagreement regarding the language that should be used.
A couple decades later, during the height of WWII, wood scarcity reared its ugly head once again, which caused demand for alternative materials, like concrete and engineered wood-based materials, to rise.
As a result, the wood manufacturing industry started to normalize thinner 2x4s.
Nearly 20 years later, it was agreed that all 2x4s would actually be 1-1/2″x3-1/2″.
In 2017, a lawsuit was brought against Home Depot and other wood suppliers, alleging that these suppliers knowingly misled consumers by not indicating that 2x4s aren’t actually 2”x4”, but nothing ever came of this.
Note: The “2×4” term being common is also because this term is easier to say (when compared to 1.5×3.5).
What is Quarter Sizing?
Lumber mills often use quarter-inches to indicate the size of roughly cut lumber.
The quarter-inches only refer to board thickness, as length and width can vary.
So how are these boards used? Well, a woodworker would most likely plane them first to achieve the desired thickness, and then they’d cut the boards to equal lengths before gluing them together to get the desired width.
To determine how thick a board is using quarter inches, simply divide the first number by the second number; the second number is always 4 (since there are four quarter-inches in an inch).
Here are some of the quarter-inch measurements you’ll see on roughly cut lumber:
- 4/4 = 1” thick
- 8/4 = 2” thick
- 10/4 = 2.5” thick
What Is Board Foot Sizing?
Board feet (bd. ft.) are often used with rough lumber, but you could see finished pieces measured in board feet.
A board foot is a piece of wood that’s 12x12x1 (144 cubic inches).
To determine how big a piece of wood is in board feet, use the following calculation: length x width x thickness divided by 144.
Need a precise answer quickly? There are calculators online you can use to find out how big a piece of wood is in board feet.
While lumber sizes might seem simple to understand, there’s actually some nuance.
The board commonly known as a 2×4 isn’t actually 2″x4″; its actual dimensions are 1.5″x3.5″, with a common span being 8′.
If you’re using the metric system, a standard US 2×4 is 38mm x 90mm.