Hardwood lumber such as oak, maple, or walnut is sold very differently from dimensional lumber and is usually measured by the board foot. Learn more about the actual thickness of plywood. Plywood is thinner than the nominal thickness as well, but for a different reason. Modern sawmills typically account for this, however, and will mill the dried boards to a more exact size, making dimensional lumber generally consistent. Today, boards are intentionally cut large to allow for shrinkage during kiln drying and the milling process.īecause the amount a board shrinks can vary by wood species, moisture content, and even the individual tree, the final size may vary slightly. Historically, softwood logs were cut green into 2″ x 4″ planks but would naturally shrink as the boards dried out, and after planing and milling, they ended up around 1-1/2″ x 3-1/2″. Why is dimensional lumber smaller than the nominal dimensions? If the nominal size is 8″ or larger, then the actual size of the board will be 3/4″ smaller.If the nominal size is larger than 2″ and smaller than 8″ then the actual size is 1/2″ smaller than the nominal size.If the nominal size is smaller than 1″ then the actual size is 1/4″ smaller than the nominal size.If you’re stuck without a tape measure or reference table, you can also use a simple rule of thumb to determine the actual size of dimensional lumber. Table showing the nominal size and actual size of dimensional lumber in inches and millimeters Nominal Size The table below shows the actual size versus the nominal size of various dimensional lumber products. The board is advertised and sold using nominal dimensions, which are a bit larger than the actual dimensions.

The actual sizes of a board are smaller than that.įor example, a 2×4 board is actually 1 1/2″ x 3 1/2″. These are the dimensions of the green board before it’s been dried and milled. Dimensional lumber is lumber that has been dried and milled to standard dimensions and is most commonly used for framing and construction.ĭimensional lumber is sold using what is referred to as the nominal dimensions of a board. Most softwood lumber sold at the lumber yard or home improvement store is dimensional lumber, such as pine or Douglas fir. Wood and lumber are no different, and for most dimensional lumber, you will find that the material is sold and listed by its nominal size, rather than its actual size. For some, it’s historical while others may be in the way they are designed to be installed. In fact, most building materials are sold by nominal, rather than actual, sizes for a variety of reasons. Hopefully, you haven’t been burned by assuming that a 2×4 is actually two inches by four inches but if you have, know that you’re not alone. You may have seen framing lumber and softwood boards sold by listed dimensions that don’t match the actual size of the board.

3 by 3 inches actual size