Trade education and workforce development are two initiatives we value highly here at Dunn Lumber, so it should come as no surprise that we have close ties with Seattle Central College's Wood Technology Center (WTC). With roots dating back to the early 1900s, WTC's history intersects with ours at Dunn Lumber at various points (our very own Ed Dunn Jr. took some classes at Edison), and we're proud to be connected with such an exemplary educational institution.
Throughout the episodes in this series, we'll be speaking with Dave Borgatti, a long-time faculty member at the WTC, about the center's history, program offering, and various topics in woodworking education. Dave got his start in woodworking as a boat builder in Portland, Oregon, for Schooner Creek Boat Works, and ended up at WTC as an instructor in 1992. Since then, Dave has helped countless students—from boat builders to carpenters and cabinetmakers—learn the woodworking craft.
Just about everyone in the construction industry knows that a two-by-four doesn't actually measure two inches by four inches—but for homeowners and DIYers, the difference between nominal and actual lumber sizing might not be so obvious until it leads to a miscalculation.
In today's discussion with Dave, we gain a better understanding of the difference between nominal and actual sizing, learn about the lumber drying and surfacing process, and pick up a couple of tricks and best practices along the way. Watch our conversation in the video above or read on for a detailed recap.
The difference between nominal and actual lumber size
Most people know what a two-by-four is, but far fewer know that it actually measures 1 ½" by 3 ½". So—why call it a two-by-four at all? Because two-by-four is its nominal size; or, the size it starts as when it's rough-cut, before it's dried and surfaced. Dimensional lumber goes through many phases of processing before it reaches the lumberyard, so referring to it by its nominal size helps keep things consistent.
This discrepancy between name and size exists with all dimensional lumber, not just two-by-fours. After being cut to its nominal size (what we call a "rough" or "green" cut), dimensional lumber is run through a dry kiln to achieve a targeted level of moisture content (sometimes listed on the grade stamp), and the board shrinks during the process. It's then surfaced down to sizing standards. These two processes can take up to ¾" off of a board.
How to calculate actual lumber size
The amount a piece of rough-cut lumber loses in the drying and surfacing process depends on its size: greater dimensions lose more, smaller lose less. While seasoned contractors and woodworkers are comfortable adjusting nominal sizing for their projects, it can be a lot more confusing if you're new to working with wood. (In fact, the confusion surrounding nominal-versus-actual sizing resulted in a $1.6 million fine to Lowe's California stores after consumers sued for misleading labels.)
Luckily, calculating actual lumber size from its nominal size is easier than it might sound. Lumber sizes are standardized, so all you have to do is remember three measurement ranges:
- Lumber less than 2" loses ¼" in width or thickness
- Lumber between 2" and 6" loses ½" in width or thickness
- Lumber greater than 6" loses ¾" in width or thickness
Common nominal vs. actual sizes
- One-by-two (nominal) = ¾” by 1 ½” (actual)
- One-by-three (nominal) = ¾” by 2 ½” (actual)
- One-by-four (nominal) = ¾” by 3 ½” (actual)
- Two-by-two (nominal) = 1 ½” by 1 ½” (actual)
- Two-by-eight (nominal) = 1 ½” by 7 ¼” (actual)
- Four-by-four (nominal) = 3 ½” by 3 ½” (actual)
- Four-by-six (nominal) = 3 ½” by 5 ½” (actual)
Buying rough vs. surfaced lumber
Depending on your project and tools, you may prefer to work with rough wood rather than surfaced. For instance, woodworkers or boat-builders with planers, table saws, and jointers might prefer to surface their own boards to specific dimensions.
Meanwhile, construction materials (i.e., framing hardware) are fabricated based on actual lumber size standards, so carpenters depend on consistent surfacing and sizing standards to make their work as efficient as possible.
Kiln-drying and moisture protection
The kiln-drying process substantially speeds up lumber-drying time. Before dry kilns were developed, lumber had to be air-dried, a process that takes about a year per inch. Operating a kiln today requires skill and precision—drying too much results in warped or cracked wood.
Some lumber (usually more expensive boards) is treated with a waxy paint on the ends after being kiln-dried. This treatment reduces the moisture that seeps through the end grain, limiting movement and helping to prevent checking.
There are a lot of nuances when it comes to working with wood. A refresher on the basics and best practices is always beneficial—whether you've been in the business for a decade or a day—and we're grateful to have friends like Dave who share their expertise with us. If you want to know more about the quality of lumber products we carry at Dunn Lumber, read the story behind our signature blue-end studs, and this look how our treated lumber products are made.
Be sure to check out the introduction to the Wood Technology Series and our conversation about the benefits of working with engineered lumber.