So what actually is the size of a 2x4?

The most well-known piece of lumber is the 2x4, pronounced two-by-four. It’s mostly used in the framing of houses but you’ll also see it in just about any other construction or DIY project.

But there is a caveat will calling a 2x4 a 2x4: It’s not really two inches by four inches as its name implies. A 2x4 is actually 3-½ inches by 1-½ inches. Many of you know this, but why is this a thing? You don’t go to Subway and pay for a $5-footlong expecting to get 11 inches (although many of you will argue this is the case). And it’s not just a 2x4: A 1x4 is actually ¾ inches by 3-½ inches; a 4x4 is actually 3-½ inches by 3-½ inches. Most of us that know about this dimensional discrepancy will say “This is how it has always been.”

But there is a reason. Put simply, the discrepancy in sizing comes from the need for the lumber industry to stay competitive with other market alternatives during times of scarcity.

Before mass production of lumber and wood started around 1870, trees were cut and made to order for carpenters. Sizes always varied, which left final sizing measurements up to the builders on site. Trees were grown and used locally and many people in the industry viewed lumber and forests as an unlimited resource in the U.S.

But as the population in the United States grew, so did building. And these once “unlimited” resources were starting to become scarce. Prime forestland was concentrated around major U.S. cities like New York, Boston, Baltimore, and Philadelphia as these areas were transportation hubs. But these forests around these cities were becoming clear.

With resources in these areas becoming scarce, other areas of the country saw this as an opportunity to enter the market. The advent of the railroad made it possible for other cities to ship lumber to different parts of the country. Cities like Chicago, Albany, NY, and Bangor, ME became lumber capitals of the country.

Competition occurred among regions, or more specifically, among species. For example, southern pine forests called “pineries” consisting of shortleaf pine, slash pine, longleaf pine, loblolly pine, and other less common species (collectively known as southern yellow pine, SYP) competed against western Douglas fir, western hemlock, and spruce forests.

At the turn of the 20th century, lumber was commonly sold as “free on board” or FOB, meaning the purchaser was responsible for shipping. According to the U.S. Department of Agriculture’s “History of Yard Lumber Size Standards,” shipping charges, determined by distance traveled and weight, doubled the cost of lumber. Thus, the density and moisture of wood began to have a big impact on forestry economics. People in the industry preferred thinner, lighter sizes for longer hauls. They produced optimal finished sizes of preferred species by kiln drying to control moisture content.

There were other factors that played a role in moving towards smaller sizes: The same technology used to power steam engine trains was now being used in the newly invented circular saw, made to achieve faster, continuous cuts in the sawmill. This development went hand-in-hand with the evolution of framing building. Wood was no longer cut from trees and shipped directly to a job site. Small dimension stock, like the 2x4, was now being used more and more.

And with the increased use of “common” lumber, the need for a uniformed sizing became apparent. As retail lumberyards pushed for more regulated measurements and standards, trade associations were formed. And in April 1919, attendees of the first American Lumber Congress called for size and terminology standardization. Although disagreement about specific language persisted for decades.

Then came World War II. The demand for pallets and crates for the war caused a shortage in wood for the lumber industry. Builders began to use alternatives to wood such as concrete block and engineered products (like plywood). People in the forest industry were under immense pressure to figure out how to become more efficient and compete. The lack of resources forced a compromise because thinner 2x4s were a way to compete with these alternatives in the industry.