Why is a 2x4 not 2" by 4"

Cecil's Columns/Staff Reports
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Cecil:

I have read your columns for nearly 35 years in and outside of Chicago. And like most fine wines, you do get better with age!

I work in the “lumber industry” and want to clear up some misconceptions about wood and lumber for your loyal readers.

Most of the lumber we are all familiar with that is available in HOME DEPOT, LOWES, HANDY ANDY, MENARD’S, Lee Lumber, Belmont Lumber etc., is generally classified as “building material. This means 2 by something (2x4) where the actual dimensions are 1.5” thick and 3.5" wide. The 2x4 and so on are called nominal dimensions. Lastly, most building material lumber found in these places is called a “softwood” as opposed to a.

The primary distinction between softwood or hardwood relates to the facts that the first is a conifer or evergreen and keeps its needles all year long. Hardwood on the other hand loses its leaves each fall.

Softwood sold as building materials are quickly cut from each log by the sawmill into nominal sized lumber that is processed and then surface dried. After which it is sent directly to the customer. The Moisture Content of softwood for use as building materials is generally 12-15%. As compared to hardwoods after kiln drying, this is extremely wet.

Hardwoods are cut for thickness, width and length by the mill, sorted for grade and then kiln dried to a moisture content of 6-8%. The difference with hardwoods is that commercially the 4/4 system of measurement refers to THICKNESS ONLY of unsurfaced wood. Unlike hardwoods, softwoods are sold by a nominal dimension and can be “managed cut” from the logs available at the mill. To the contrary, all hardwoods are cut from GRADE and yield according the individual log being cut at the sawmill.

Kiln drying hardwoods to a 6-8% moisture content by weight removes water from the wood and is necessary so that beautiful mouldings, trim and other natural hardwood products in your home or office do not disintegrate in place. Kiln drying is not necessary for softwoods used a building materials because the finished product will be used outside anyway and not where the normal interior temperature and humidity swings found inside a home or office are present.

The point of this comment is there are really TWO types of lumberyards. All of the building materials yards are discussed above. And yet there are the less numerous and harder to find Hardwood Lumber Yards. So if you want 5/4 (1.25 actual thickness) pine, the Depot and other such places will have it. But if you want some ash to make a spindle or runner for Aunt Maize’s rocker, you need to find a genuine hardwood lumber yard.

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I have a different observation about today’s (10/12/2012) column about lumber sizes: Here, Cecil mentions that his knowledge of lumber derives, at least in part, from his experiences in rehabbing old houses (his own, in particular), and specifically from his examination of the lumber sizes in the rafters and studs.

Elsewhere we see a forum on these boards in which Ed Zotti discusses his experiences in rehabbing old barns or whatever.

Have we an inadvertent confession here, or at least a significant chunk of new evidence, that Ed == Cecil?

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I’m just old enough to remember a lumberyard worker in Central Maine, ca. 1955, complaining that you couldn’t get decent “pre-aged” wood, anymore. This, I was told, was the reason that the door to my bedroom, in our brand-new house, wouldn’t shut properly.

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Great reply, WWL.

Adding a link to Cecil’s column helps the reader to follow along.

Why aren’t two-by-fours two inches by four inches?

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I remember reading an article by an experienced architect who described getting drawings of a house from a architect newly graduated from college. The experienced architect thought there was a problem with the drawings but couldn’t immediately identify what it was. Eventually, he realized that the novice drew the plans assuming that 2x4s were actually two inches by four inches. The point of the article was the difference between what is taught in school and how things work in the real world.

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Cecil,
Hi, I’m new to your Straight Dope.
With regards to wood sizes I thought raw timber was usually first aged and then cut to a larger than stated size to allow for ‘machining’ to the standard size (actual) as stated. At least I think that’s how we do it in Aus.

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The end result we call 'dressed’timber

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As a side note, another way to get a 'true-size" 2x4 or other size is to ask for ‘rough-cut’. You can get those in a few places around here (metro-Boston MA). It really is ‘rough’ - not with the smooth finish we’re used to from the big-box home centers. I had to do that once to replace a section of fence made with true-size lumber.I used 2x12 and 2x8, but the thickness was important.

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building framing used to be (more than half a century) done with the rough cut or full dimension timber. you need to adjust when repairing or reusing when mixing types.

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Well over half a century, since I remember having all this explained to me by my father (who was not in the business, so someone would have had to have explained it to him) almost sixty years ago.

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What kind of answer was that?

I love your website and your answers to questions, but come on, you could have done a little research, maybe asked an actual carpenter or sawmill.

Forget all the history Cecil mentioned about money hungry individuals, the correct answer is.

A 2"x4" TODAY is still 2" by 4". That is rough cut size, which you can by from any sawmill. The material you by at the lumber store is graded, dried, and finished.

Finished means planed down so every board is exactly the same size. End product is 1 1/2" x 3 1/2". This applies through all nominal dimensions.

5/4 boards are relatively new in the building industry (20 years) and there is different suppliers out there that call them 5/4 when there not. 5/4 is 5/4" thick by 5 1/4" wide, and yes they are common at a proper lumber supplier. If your curious ask and I will tell why they came into existence. :slight_smile:

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Hello Moryn - welcome. Is thisthe column you are referencing?

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MODERATOR NOTE: Moryn, welcome to the Straight Dope Message Boards. Since there was already a thread on this topic, I have merged your thread (started yesterday) into the existing one. No prob on our part, I hope ditto on your part, just makes it easier for readers to have all of one topic together.

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5/4 lumber is readily available in almost any width. What you are describing is a somewhat standard 1 x 6 board. A “standard” would only be 3/4 inch thick because of finishing, while the 5/4 will end up truly 1 inch thick after finishing.

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Isn’t this basically what Cecil said?
Powers &8^]

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My understanding is that a modern sawmill initially cutting a nominal 2x4 (i.e. finished 1 1/2" x 3 1/2") will cut it smaller than 2"x4" (maybe 1 7/8 “x 3 13/16” or something), as modern drying and planing methods are more precise and don’t lose a full quarter inch from each side (and saving that 1/8" of material adds up eventually). So a ‘rough cut’ actual 2"x4" board is not the same as a rough cut board intended to be a nominal 2x4.

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LalalalalalalalaI’mnotlistening.

NO! It’s just another of the many reasons Little Ed and Unca Cecil get along so well.

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Yes, like there are only two journalists in the world who are interested in rehabbing old buildings. Gimme a break.

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We renovated an old house that had joists that were truly 2" x 4" and oak at that. They weighed at least four times what modern lumber weighs. The 100 year old scraps burned frightenly fast.

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Talk about discussion about nothing. 2’‘x4’’ is the measurement before it is machined or dressed. If you puchase 2’‘x4’’ timber undressed it should measure that and usually does in my experience.