The Spruce
Dimensional lumber has two size categories for width and thickness: nominal size and actual size.
Dimensional lumber is wood lumber cut to pre-defined, standard sizes.
A two-by-four (2x4) is an example of dimensional lumber.
The Spruce
Nominal Size vs. Actual Size
Dimensional lumber has differing nominal and actual width dimensionsfor the same-sized board.
Instead, it is 1-1/2 inches by 3-1/2 inches.
Tip
In rare cases, nominal and actual dimensions will match.
Some older homes may have nominal dimensions two-by-fours, measuring 2 inches by 4 inches.
It’s uncommon, but you may find this when remodeling a home.
Dimensional Lumber Sizing
Softwoods used for building framing have the following nominal and actual dimensions.
These dimensions do not apply to laminated veneer lumber boards, hardwoods, or floorboards.
Softwoods includeDouglas fir,spruce, or hem-fir (a mixture of western hemlock and Amabilis fir).
Lengths are typically shown as the last number.
A typical dimensional lumber designation might read: “2 in.
x 8 ft.”
This can be confusing because it combines nominal and actual sizes.
The first two numbers (2 inches and 4 inches) are nominal widths and depths for the lumber.
As stated earlier, their actual sizes are 1 1/2 inches and 3 -/2 inches.
Yet lengths of dimensional stock are always expressed asactual sizes.
So, this example board’s actual length is 8 feet.
When you take that “2 in.
Dimensional Lumber Basics
Dimensional lumber is sawn, planed, and sometimes further smoothed to standard sizes.
Standardization means that all builders and do-it-yourselfers use lumber sized the same way.
When building or remodeling homes, two-by-fours are typically used for walls.
Two-by-sixes or two-by-eights are often used for floor joists or ceiling rafters.
The term “dimensional lumber” is rarely used at lumber yards orhome centers.
For the average do-it-yourselfer, most long, thin lumber used for building is considered dimensional lumber.
Four-by-fours (4x4) are typically used as fence posts.
Dimensional lumber comes in standard sizes and is used for building projects and remodeling homes.
However, dimensional lumber is more affordable than engineered lumber, a highly processed lumber-based product.
There are limitations to using dimensional lumber.
Older types may not be compatible with newer wall systems, making them difficult to reuse.
Cedar is a good option since it is affordable and ages well due to its natural oils.
However, softwoods like pine and poplar deteriorate quickly if left untreated and must be painted or stained.
Expensive hardwoods like walnut and mahogany age well but are more costly.
