Let me rephrase my question Why is a 2x4 called a 2x4 when i is really 1 1/2x3 1/2?

Answer 1

This is a two part answer. Some of the earlier posters have hit on one part, some the other but it takes both to make a 2X4 1 1/2X3 1/2.

A 2X4 is a "nominal" 2" X 4", it is 2" X 4" in name only. It was given this name due to the fact that rough cut lumber was at one time commonly cut 2" thick and 4" - 14" wide in 2" increments. The first reduction in size came when the practice of finishing lumber by planing and drying before distribution came into being. This reduced the actual size of the lumber to 1 3/4" x 3 3/4". If you get into an older house (1910 - 1970ish) built with finished lumber, you will find that new lumber is smaller.

The second reduction came about at a later date, reducing the "net" size of a 2X4 to 1 1/2" X 3 1/2". As an earlier posted mentioned, this was sold as a conservation effort. Regardless of the intentions, the large lumber mills benefited by increasing the amount of finished lumber that could be manufactured from any given tree.

Nearly all lumber is stated in nominal sizes -- 2" is 1 1/2", 4" is 3 1/2", 1" is 3/4". Lumber is available 2" net thickness, but it is called 10/4 -- 10/4 reduces to 2 1/2, 2 1/2 dressed is 2". 5/4 is a full inch thick (commonly seen as decking boards, but certainly available in many other forms.

Plywood is also nominal size, 1/2" plywood is actually 15/32", 5/8" is 19/32", 3/4" is 23/32", etc.

It should be noted that a 2 X 4 is no longer planed from a 2" X 4" piece. Due to advances in milling technology and the desire to reduce the amount of wood used to make lumber further, the lumber is oversized 1/8" or less before planing, so a 2X4 would be cut to 1 5/8" X 3 5/8" or less then planed to the net size. You can still buy a 2" X 4" net rough cut, but usually from smaller local mills.

Also, an entire log is no longer cut into pieces of the same dimension. It is really cool - a computer images the log as it moves down the line and determines the optimal cuts to make to get the greatest value from the log.

Another poster indicated that several building materials would be cut from the same log. Bark is used for mulch, but other than that logs are pretty much single purpose. Different species and different grades of trees have different uses. Plywood is made from veneer logs, which are peeled as was indicated. The leftover core is rather small and may make a single landscaping timber (the rounded edges are a result of this process) or a single 8' 4X4, but not lumber. OSB chips are made from trees grown specifically for the purpose. Early variations were called Aspenite because aspen pine was the material of choice.

Sorry, got long winded. Hope this clears the situation a bit.

Answer 2

It is a 2 inch by 4 inch board prior to it being planed. It has nothing to do with the sheet rock. Years ago a 2x4 was actually planed at 2" x 4" as wood got more expensive the size was reduced. Any board you buy now will be 1/2" smaller than what it states, except for fine finish boards which are more expensive and are sized to exact dimensions.

Answer 3

The dimensions used to describe dimensional lumber are rough-hewn measurements. When lumber is being cut from rough timber it goes through a number of stages.

The log is first debarked, the chips and shavings often being used in bark-mulch for landscaping purposes. The log is then pared down to a uniform diameter. Chips are used in the manufacture of Oriented Strand Board (OSB), a product often used as a substitute to plywood. Then the log is then peeled, the 1/8 inch thick peelings are used in manufacturing plywood. Then the log is run through a large blade, making the log square. At this point, the dimensional lumber is extracted.


In the case of a 2 x 4, it is usually the last dimension extracted from the log; the strip of lumber measuring 2 inches by 4 inches. The log will be rotated several times during this stage, ensuring that the grain of the lumber basically runs perpendicular with the longest dimension.

Once the lumber is cut, it is either classified as rough-hewn lumber or is sent through a planer which reduces the dimensions of a 2 x 4 to 1 1/2 x 3 1/2; however it is classified as a finished 2 x 4.

The same applies to other dimensional lumber. A finished 2 x 8 actually measures roughly 1 1/2 x 7 1/8 inches.

Answer 4

It was made from a piece of wood that was 2x4 with rough sides. After it was planed to size it was smaller but smooth-sided.

Think of it like a McDonalds Quarter pounder which weighs a quarter pound when it is raw but a lot less after it is processed.

Answer 5

actually, the 2x4 came as just that prior to 72, when the american socioty of engineers determined that there was no signifigant reduction in strength, while reducing the number of trees killed each year by the lumber industry. It was a good compromise for both the tree huggers and the loggers due to high fuel costs causing high expenses in the forest, as well as the the great reduction in acreage harvested per billion board feet produced. 1974 it was actually noted that acreage of forest in the US had not changed based on national economic and ecological survey, and in 2004 the net acreage of forest exceeded what was estimated to have existed in the 17th, 18th, and 19th centuries, although almost none of the old growth forrest on the eastern seaboard exists anymore. On a side note, the American logging industry is responsible for the increase in net forrested acreage.

Answer 6

It's also sounds better to say "Someone needs to hit him upside the head with a 2X4" then "Someone needs to hit him upside the head with a 1 1/2"x 3 1/2".

Answer 7

it is called a 2x4 becasue, those were the measurements of the wood before it was planed down.

Answer 8

jesse is right, absolutely.

if you want to have a 2x4 in exact measurement. buy raw wood from a lumber yard and you plane it yourself

Answer 9

Round up! And don't forget to carry the one. ;-)

Answer 10

what the heck because its easy to say get it