Why is a 2×4 not actually 2″x4″?

Today we answer a life’s persistent questions – Why is a 2×4 not actually 2″x4″?


This is enough mystery to drive some people up a wall, but today we’ll shed a little light on just how this conundrum came about. That boring old 2”x4” which isn’t actually a 2”x4” has a lot of history behind it. Let’s take a little ride back to the 1800s!

History of Lumber Sizing

We’ll begin in the wild wild west. During the early 1800s most wood was cut and then used locally – heck, most men just built their house with their own two hands from tree to cabin – Charles Ingalls style. As the country developed, sawmills popped up to satisfy local building demand. It was roughly sawn, not dried (otherwise green wood), and lumber sizes varied based on local customs or whoever was doing the cutting.

Word of the day: Green wood

Green wood is freshly cut wood that has not been kiln dried. Different species of wood have different moisture content and wood in different areas also varies. IE: Wood in Portland where it’s wet will have a lot more moisture than in Phoenix. Today, all lumber is kiln dried. We’ll get to why in a minute.

Eventually, as the lumber industry developed a lot of demands began to be placed on sawmills.

“We want cheap, uniform size lumber and we want it everywhere!” said pretty much everyone in the world building everything we see today.

At the time, 2” became the standard based on demand, but still had a lot of variation in the measurement, mainly because there was no way to control it. Think about all the different types of wood out there, then consider that each has differing level of moisture depending on type and where it has come from. So even though it was probably a 2” board when cut, once dry, was significantly smaller with no way to predict what the difference would be for different trees or types of wood. When the railroad came into play sawmills quickly realized that green lumber with a lot of moisture in it was much heavier and more expensive to transport. Dried lumber also worked better for construction because it was stronger and wouldn’t shrink over time. They don’t say necessity is the mother of invention for nothing – kiln dried wood is now a thing!

Another invention – planing, also played a role our elusive “Why is a 2×4 not actually 2″x4″?” question. Planing answered the demand for uniform sized wood. Planing smoothed one or more sides of the lumber, made it easier to handle with less splinters, and also – you guessed it – even smaller. By 1961 – enough was enough, and standards were put in place. However, standards maintained the already messed up thing that had become the norm – a 2”x4” that is not actually 2”x4”, imagine that. You may not like the answer any more than the question, but that’s that.

If your OCD still has you wanting a true 2”x4” – let’s see what we can do about that. It just so happens that we are experts in tree removal, so that’s probably where you’ll have to start – all the way back in the 1800s, tree to cabin like. If you need help with tree removal anywhere in Portland or the surrounding areas give us a call. Otherwise, you may end up looking like this.  


Then, you’ll be on your own to try to figure out how to cut a board from green wood slightly bigger than 2’x4” but that will shrink to exactly that once dry. That seems like a much tougher question. Good luck!

P.S. – To save the hassle, just tell the lumber clerk you want a “true size” 2”x4” or whatever dimensions you are looking for – those are the magic words!

Lumber photo by Bureau of Land Management (Oregon_BLM_Forestry_10Uploaded by russavia) [CC BY 2.0], via Wikimedia Commons

Tree cutting photo by Superior National Forest [CC BY 2.0], via Wikimedia Commons

Sources:USDA Forest Service, Wikipedia, Wood Central, and Straight Dope

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