Standard Dimensions of Softwood Construction Lumber

Construction softwood lumber is generally made from conifers, or pine trees.

Construction lumber made from softwood such as fir, spruce, or other pine and conifer trees is sized according to accepted standards for nominal dimensioning of wood building products. The American Softwood Lumber Committee (ASLC) Standard PS-20-10 is the 2010 guideline, as provided through the National Institute of Standards and Technology (NIST) and the U.S. Department of Commerce.

ASLC Standard PS-20-10

PS-20-10 is based on "Procedures for the Development of Voluntary Product Standards"; U.S. Dept. of Commerce

The American Softwood Lumber Standard PS-20-10 is intended to establish nominal sizing criteria, green lumber and dry lumber comparison data, design value assessments, commonly used terminology, grade-marking requirements, and other information relating to softwood lumber. The terminology used to describe lumber size is known as the "nominal size."

Nominal Softwood Construction Lumber Dimensions

Lumber manufacturers trim lumber to fractional dimensions from "nominal" sizes.

Softwood construction lumber is sized in whole inches, even though actual sizes are smaller. This is due to the trimming process manufacturers use to provide consistency and finish. Typical pine studs used for constructing interior partitions are usually called "2 by 4's," which indicates they began (in rough-cut size) 2 inches thick by 4 inches wide. Processing then trims them to about 1.5 inches by 3.5 inches. Likewise with all structural softwood lumber dimensions.

Considerations

When wood dries out, it shrinks in size.

Softwood construction lumber sizing is not necessarily "cast-in-stone." Tolerances in the manufacturing process are fairly forgiving, thus it is not uncommon to find a "2 by 4" that actually measures 1 3/8 inches by 3 3/8 inches; even smaller than what the standards might recommend. In addition, moist (green) lumber might originally measure larger than it will after it dries out.

References

• Sizes.com: Softwood Lumber Sizes
• NIST: PS-20-10
• AmericanLumberStandardCommitteeInc: Lumber Program