“Why is a 2×4 not a 2×4?” you wonder as the actual lumber falls short of your estimates for do-it-yourself or DIY projects. Did lumber manufacturers get the boards’ measurements wrong? Or have they intentionally sold a smaller board?

It is neither the lumber manufacturers nor the hardware store that came up with lumber that has an actual size smaller than its nominal size.  Quite simply, the resulting true dimension is a result of milling and planing. So, let’s find out 2×4 Actual Size.

2×4 Actual Size: Why Is a 2×4 Not 2×4?

The 2 × 4 being sold is actually 1 1/2” by 3 1/2.” There is a difference in actual and nominal dimensions because pine and other timber shrink after it is milled and planed. In planing, we flatten, reduce the thickness of, and impart a smooth surface to a rough piece of lumber or timber.   These give wood a smooth finish and have it conform to the standard size.

Listed vs Actual Dimensions 

2×4 is the generic term because it’s easy to remember, even though the actual dimensions of the board are 1½ inches by 3½ inches. Lumber mills also round rough edges to reduce injury.

This is true for the dimensions of other boards, whether or not they come from pine or cedar. That’s why lumber sizes become smaller than their nominal dimensions.

Listed SizesActual sizes
1 x 23/4” x 11/2”
1 x 33/4” x 2 ½”
1 x 43/4”x 3 ½”
1 x 53/4” x 4 ½”
1 x 63/4” x 5 ½”
1 x 83/4” x 7 ¼”
1 x 103/4” x 9 ¼”
1 x 123/4” x 11 ¼”
5/4 x 61 (1/8)” x 5 ½”
8/4 x 61 3/4” x 5 ½”
2 x 41 1/2” x 3 1/2”
2 x 61 1/2” x 5 1/2”
2 x 81 1/2” x 7 1/4”
2 x 101 1/2” x 9 1/4”
2 x 121 1/2” x 11 1/4”

Rough Lumber vs Plane Lumber

Planed boards’ flat surface is ideal as a work area – for shelves and kitchen work surfaces. Moreover, planed surfaces make for stronger, neater joints. Plus, you save on the time and effort of doing the planing yourself.

These are the types of planed boards:

Planed All Round –  four sides of the board are passed through the planer. This is used when all sides will be visible and you need them to be smooth.

Planed Single Edge – only one side of the board has been smoothed; ideal for flooring or external cladding.

Planed Both Sides – only both of the wider surfaces are planed. This can be useful for flooring verandas or internal balconies. 

Rough lumber (or rough sawn lumber), has its advantages. It’s always priced lower because after being felled from trees, the board has not been treated or smoothed. Rough sawn lumber is best used as internal frames. 

From Local to Crossing Great Distance

To understand lumber sizes today, we must go back to the olden days. Then, the construction industry sourced lumber from the nearest manufacturer.

At this point, there is not a bit of need for the lumber industry to set a standard on lumber sizing. Every lumber manufacturer adheres wood dimensions to the needs of the community. And in case the actual lumber doesn’t fit, the builder remedy the discrepancy.

This changed at the end of the 19th century. Since there was no forest service to regulate the cutting of trees, forests diminished and became farther from towns and cities. That’s why construction projects sourced wood from out of town. It became obvious the lumber had dimensions that varied from one another and were cut in different sizes. The different cuts caused carpenters to complain.

Dimensional Lumber Emerges

To deal with carpenters, some lumber mills began to cut and plane dimensional wood in uniform sizes. What we call ‘surfaced one side’ or S1S and ‘surfaced two sides’ emerged. Carpenters can even request wood that is ‘surfaced on four sides,’ but they have to pay extra.

The practice was convenient for builders and also encouraged manufacturers and traders to cut the wood into uniform sizes and plane them. This was when lumber associations set the size standards for lumber. Yet, this standardization varied per region.

The change began after World War 1 and the demand for lumber surged, buoyed by home construction (that’s why we see 2x4s in old homes). This prompted the holding of the American Lumber Congress in 1919.

During this time, a committee found it necessary for the lumber industry to have standards on the lumber sizes, grades, moldings, forms, and nomenclature. Then in 1921, the industry (manufacturers, wholesalers, and retailers) decided on the size standards. This is when the 2 inches by 4 inches wood and the other sizes came about.

How Lumber is Made

Apart from planing, the difference in the nominal and actual dimensions is a product of the wood’s manufacturing process – from felling to banding. Regardless if it’s pine or cedar, here are the steps in making lumber:

Felling– After the trees are cut, the tree trunk is further cut to sizes fit for transport. The trunks are transported to the lumber mill and are stacked into piles (commonly called log decks). Water is sprayed on them to prevent drying. 

Debarking and bucking– From the pile. a rubber-tired loader picks up the logs to the mill. The tree’s outer bark (regardless of its pine or redwood, for example) can be removed and burned as fuel for the mill’s furnace. This can also be sold as mulch. After this, the lumber is cut into seven or eight pieces, then these are cut in half.

Head rig sawing large logs– The log is placed in the mill. Sensors then tell the dimension of the desired lumber, and if there is any defect. Then, a computer comes up with a cutting pattern to achieve the desired dimension and maximize the lumber.  A head rig saw cuts the log according to the cutting pattern, producing flitches (large planks). The first cut (called slab) will be used as paper pulp.

Band sawing small logs– The smaller logs are passed through a series of band saws. With this, you’ll have logs that measure an inch, two, up to four inches in one pass.

Resawing– Large cut pieces (commonly known as cants)  are then placed in a chain conveyor and pass through multiple-blade bandsaws. The rough-cut pieces are then cut into desired widths (2 inches by 4 inches and the like) and the edges are trimmed square. If the pieces are small enough they will not be cut but may pass through a chipper that will level the square edge.

Drying or seasoning– The resulting pieces (called green lumber- still moist and prone to warping and bending) are then moved to a drying area. The drying process prevents the lumber from decaying or shrinking. The lumber may be air-dried (in this, the wood is stacked carefully and left for the air to dry it) or kiln-dried.

Kiln drying is when wood is dried using an oven (kiln). With this, you can control the humidity, temperature, and steam. With the kiln, drying is faster and the wood comes out with the desired moisture content. 

Planing– Rotating heads cut the dried to their final dimensions, smoothen surfaces, and round the edges. 

Grade stamping and banding– Every piece of lumber is inspected. Then its grade, moisture content, and mill identification number are stamped on it. These are grouped into bundles according to the type of wood and grade. These are then sold to lumber yards.

2×4 as Framing Lumber and for Other Projects

2 x 4s stand out because of strength and versatility. That’s why they are good for framing houses and in part of just about every other type of project. As long as it’s not required to bear the weight of any woodwork, you can use it as framing lumber. Great examples are lumber from spruce pine fir and Douglas fir. Spruce absorbs moisture more slowly than pine sapwood. Plus, the grain of the spruce is easy to plane.

Framing lumber – 2 x 4 is the most popular framing lumber. You use it to maximize space. Although 2×6 will make your home stronger, using this will just increase the cost. And since 2×6 dimensions are wider, you’ll get less space.  Plus, with 2x4s as dimensional lumber, you’ll have an interior that is four inches deeper, enough for plumbing and wiring between the studs.   

Other projects – 2×4 however, is not only good as dimensional lumber. If you have a stock or a couple of pieces, you can use these for the following:

  • Bench
  • Plant wall
  • Storage shelves
  • Bar stools
  • Coffee table
  • Bike rack
  • Tool stand
  • Desk with drawers
  • Kid’s picnic table
  • Small step ladder

But beware: 2x4s are not the ideal materials for furniture. When they are dried, the lumber can crack, bend, warp or even harden. Instead, use lumber from hardwood such as maple and mahogany. These look good and can last a long time.

You might want to learn more about Douglas fir vs pine lumber. Here is an article to guide you.

2X4 or 2×6 for House Construction?

As good as 2 inches by 4 inches is for framing, will it be better to use a bigger piece for house construction? We compared both in a number of aspects.

Strength–  Neither contributes to the house’s strength. By itself, 2×6 is stronger, but 2×4 has enough strength (at less cost) and already makes a home structurally sound. Plus, you won’t utilize 2×6’s strength, as the frame components are usually installed farther apart.

Insulation– At first glance, 2×6 has the advantage. This is because, with the added depth, you can have more insulation and restrict airflow. Note, however, that this will matter if the builders will indeed add insulation material, which they usually do not. Thus, the theoretical does not necessarily translate to actual, more insulation.

Cost– 2×6 costs more. With 2 inches by 4 inches, framing studs are at about 16 inches on-center. This is less than the 16 inches on-center standard for 2×6. Thus, you’ll need more studs. You’ll also spend more on window and door extension jambs, top and bottom plates, and window and door extensions.

Size– Using 2×6 results in a smaller home. 

Bottom line:  You’re better off using 2 x 4s in-house construction. You can opt for 2 x 6 frames if you need more room for insulation.

Maintaining Wooden House Frames

Wooden frames require little maintenance. Yet you still have to watch out for the ill effects of moisture, the weather, and pests. Here are our suggestions to minimize the impact of these hazards:

  • Check the structure regularly.
  • Wood can dry out or have excess moisture. For this, apply one or two coats of stain within two months after building.
  • The stain should let the wood breathe and keep water and moisture out. 
  • Apply the stain on posts when there are signs of fading.
  • For rafters and roof structures that are covered, apply stain every five to six years.
  • Apply insecticide and fungicide.
  • Consider using stainless steel or aluminum plates to hold timber frame posts.
  • For the interior, apply a solid stain every five years.
  • Use a humidifier indoors.
  • Ensure there’s sufficient ventilation, especially in the kitchen. This is because oils can cause wood discoloration.
  • Don’t touch the wood often. Oils from the skin can break down the stain.

Regular inspection, wise design choices, and the use of great materials in home construction are the secrets to prolonging the life of your timber home.


Why is it called a 2×4?

It is called 2×4 because it actually measured 2 inches by 4 inches – the nominal dimensions – before being planed. The name came from its exact measurements, especially when a standard set of measurements were enacted in the US in the 1920s. The name stuck, as it’s easier to remember and say, even though 2x4s now measure 1.5-by-3.5 inches.

How thick is a 2×4?

A 2×4 is 1½ inches thick after it has undergone sanding and has been smoothened. After being cut and in raw condition, a 2×4 is slightly less than 2 inches thick.

How wide is a 2×4?

A 2×4 is 3½ inches wide after it has undergone sanding and has been smoothened. After being cut and in raw condition, a 2×4 is approximately 4 inches wide.

How long is a 2×4?

A 2×4 is usually 8 feet long. This is the same length as a sheet of plywood or drywall.  There are also 2×4 that are 92 ⅝” long, or roughly 7.7 feet. The shorter length considers the thickness of the boards that you will install above and at the bottom of the wall. The little discrepancy in actual and nominal dimensions is acceptable, given we are presented with a smooth, polished, and edge-free product. We appreciate this consistency in the quality, at the same time, we can be sure the next 2×4 (which are the nominal measurements) you’ll buy will still measure 1 1/2” x 3 ½.”

Interesting read: What is the actual size of 2×8 lumber?


You no longer have to wonder why is a 2×4 not 2×4. The said measurement is only nominal, and the discrepancy against the actual size is a result of the refinement of lumber. These are also the end result of the standards set for the processing and using the lumber. 

The little discrepancy in the actual size and the nominal size is acceptable, given the end result is a smooth, polished, and edge-free product. We appreciate this consistency in the quality, at the same time, we can be sure the next 2×4 you’ll buy will still measure 1 1/2” x 3 ½.”

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