Dimensional Lumber Size Guide

Dimensional Lumber Sizes

We hate to be the bearer of bad news, but if you aren’t in the loop on this, it’s about time someone bring you up to speed. When it comes to dimensional lumber, there’s a difference between a board’s nominal size & its actual dimensions. Confusing, right? We understand, and thus, that’s why we created the Complete Guide to Dimensional Lumber.

Nominal Sizes vs Actual Dimensions

Nominal Size Actual Size
1″ x 1″ 3/4″ x 3/4″
1″ x 2″ 3/4″ x 1-1/2″
1″ x 3″ 3/4″ x 2-1/2″
1″ x 4″ 3/4″ x 3-1/2″
1″ x 6″ 3/4″ x 5-1/2″
1″ x 8″ 3/4″ x 7-1/4″
1″ x 10″ 3/4″ x 9-1/4″
1″ x 12″ 3/4″ x 11-1/4″
2″ x 2″ 1-1/2″ x 1-1/2″
2″ x 3″ 1-1/2″ x 2-1/2″
2″ x 4″ 1-1/2″ x 3-1/2″
2″ x 6″ 1-1/2″ x 5-1/2″
2″ x 8″ 1-1/2″ x 7-1/4″
2″ x 10″ 1-1/2″ x 9-1/4″
2″ x 12″ 1-1/2″ x 11-1/4″
4″ x 4″ 3-1/2″ x 3-1/2″

What is Dimensional Lumber?

Dimensional lumber is a classification for wood boards that are sold in predetermined sizes that have been standardized across the lumber industry. The most notable example would be a 2×4, which is a board of any length that has a thickness of 2 inches & a width of 4 inches (hence 2×4). The misleading part is…those aren’t the actual measurements for a 2×4’s thickness & width. Rather, those were the dimensions for the board prior to being cured & planed. Once a 2×4 has finished the refinement process, its actual dimensions shrink to 1.5″ thick & 3.5″ wide.

Now that we’ve clarified the measurements for thickness & width, it’s time that we drop another twist into the story. The measurement for length is the same for any given board’s nominal size as it is for its actual length. The reason for this is that boards typically aren’t cut to length until after they’ve been cured & planed. Thus, there isn’t any additional shrinkage involved once a board has reached this stage in the refinement process.

Common Wood Species

Generally speaking, the cheaper the wood species, the more likely it is to be available as dimensional lumber. There are definitely a few other factors at play, but the affordability of a given wood species often dictates whether or not it can be purchased as dimensional lumber. With that being said, it’s still worth discussing the other factors since they can be more influential than affordability.

For instance, wood species that are frequently used in highly regulated industries like construction tend to be available in nominal sizes. The reason for this is that standardization ensures some level of quality control & consistency. For people living in an earthquake zone, this should offer some reassurance. Additionally, the use of standard dimensions enables architects & designers to have some degree of predictability when designing a structure. As an example, you can imagine how much more difficult it would be to remodel a house if the wall studs had irregular dimensions.

Another reason for a wood species being produced in nominal sizes is to fit the needs of a certain application. For reference, redwood boards that are used for fence posts require that the board be at least 4 inches wide & 4 inches thick. Thus, it’s no surprise that home improvement stores typically offer redwood as dimensional lumber rather than in board footage sizing.

Now that we’ve rambled enough, let’s actually list out the wood species that are often produced as dimensional lumber:

  • Cedar
  • Douglas Fir
  • Oak
  • Pine
  • Poplar
  • Redwood

1-Inch Thick Boards

Dimensional Lumber Chart - Nominal Size vs Actual Dimensions

2-Inch Thick Boards

Dimensional Lumber Chart - Nominal Sizes vs Actual - 2x4, 2x6, 2x8, 2x10 Boards

Home » DIY Tutorials & Work Shop Resources » Woodworking » Lumber Guides » Dimensional Lumber Sizes

Also published on Medium.

Leave a Reply