What is Dimension Lumber?

Mary McMahon
Mary McMahon

Dimension lumber is lumber which has been cut and planed to a standardized width and height. The length can vary, with dimension lumber typically coming in an array of lengths for different tasks. This timber product is also known as dimensional lumber. The standardized measurements vary, depending on which nation the lumber is going to be sold in, but mills are required by law to use the same standards and measurements so that consumers know exactly what they are buying when they pick up lumber at the lumber yard. In the United States, for example, some common dimension lumber sizes include 2 inches by 4 inches (5.08 cm by 10.16 cm) and 2 by 6 (5.08 cm by 15.24 cm), also known as 2x4 and 2x6.

The most popular width and height measurements for dimensional lumber, which is commonly used for framing houses, are 1.5 inches by 3.5 inches -- a cut known as the two-by-four.
The most popular width and height measurements for dimensional lumber, which is commonly used for framing houses, are 1.5 inches by 3.5 inches -- a cut known as the two-by-four.

While the standard nomenclature used to refer to dimensional lumber might be perceived as a measurement of its actual size, this is not actually the case. The numbers refer to the wood when it is still "rough," before it has shrunk as a result of the drying and planing process. The actual standardized sizes are, as a result, slightly smaller than the numbers used to refer to the sizes.

Lumber yards divide materials into rough categories to help with organization and sorting.
Lumber yards divide materials into rough categories to help with organization and sorting.

Both hardwoods and softwoods are available as dimension lumber. Softwoods tend to be less expensive, as a general rule. It is also possible to purchase engineered wood products in standardized dimension lumber sizes. Depending on the type of wood, versions treated with chemicals to help the wood resist insects and rot are available along with dimension lumber which has not been treated.

Lumber mills tend to dry their wood to a standardized moisture level, which may be lower or higher than someone desires for a project. If the moisture level is too high, the wood needs to be allowed to dry further before it can be used. Using wet dimension lumber in a project means that the lumber will warp and cup as it dries, potentially compromising the project. For example, the framing of a house could bend, throwing the framing out of plumb.

In some regions of the world, very large sizes of dimension lumber are known as timbers, while smaller sizes are known as boards. This allows lumber yards and construction workers to divide the materials they work with into rough categories which help with organization and sorting. Cost of the product is usually based on length, with discounts available for people who buy large volumes of lumber and for those who do not require custom sizes.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


@matthewc23 - I am no expert on the matter, but I would guess that the price would greatly depend on the size of the deck. I have looked at lumber before for smaller home improvement projects before, and 2x4s are usually a couple of dollars. I would imagine redwood is much more expensive. That would depend on availability, too. I bet someone else here might know a little more than me.

I have always been curious about what they put into treated wood that makes it rot and insect resistant. My guess is that it would have to be some sort of fungicide, since I'm pretty sure fungi are what actually start making the wood rot. Maybe it is something that tastes bad to insects, too. Does anyone know?


Could someone please tell me the typical price to buy lumber from a lumber yard? Over the past couple of weeks, we have started talking about possibly adding a deck to the back of our house.

Of course, if we decided to do the project, we would hire someone to do it, but before we call anyone, we would like to try to come up with a rough estimate for materials and see if it would even be within our budget. I assume we would need some type of treated lumber, but that's about all I know.

We talked about maybe even using redwood lumber, since it always looks really nice. How much more is redwood than regular pine lumber? How are dimension lumber prices even calculated in the first place?


@jcraig - That is a great question, because I had the same problem when I first started with woodworking. From my experience and talking to other woodworkers, it really just depends on your location as to how you can get hold of dimensional hardwood lumber.

I started off doing a lot of smaller, decorative projects with softwoods, but then I decided to delve into making things like shelves that really should be made with hardwoods.

I am fortunate to live in a pretty rural area in the Midwest where there is a lot of forest land. About 10 miles away is a sawmill that gets all of the common trees, and even some odd species that you would never be able to find at a lumber yard. That is my source for everything from high end woods like walnut down to some of the uncommon species I mentioned like honeylocust.

For people who don't have access to local sawmills, I'm also curious about how they are able to find hardwood lumber.


Something I have always wondered is where people are able to find dimensional hardwood lumber. Any lumber yard I have been to only sells softwoods like pine lumber. Sometimes they will have a selection of oak lumber in small sizes, but these wouldn't be big enough for every project. The types of wood are very limited, too.

Obviously, there are places to buy things like maple, walnut, and oak lumber, but I have yet to figure out where. In some projects like kitchen tables, people will end up with huge, solid sections of lumber. I'm not looking for any type of dimensional hardwoods, but I'd just like for someone who knows more to please tell me where it comes from.

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