![]() ![]() Early pipe manufacturers made the walls in the smaller sizes much too thick, and in correcting this error in design, they took the excess from the inside to avoid changing the sizes of the companion fittings.įor sizes larger than 12-inch, NPS corresponds to the actual outside diameter. The table below cross-references the nominal dimension of a PIPE with its actual outside diameter.įor sizes from 1/8-inch through 12-inch, the NPS corresponds to the nominal inside diameter, but differs somewhat from its actual inside diameter. ![]() For example, a 1-1/2″ pipe size actually has an outside diameter of 1.9″ NOT 1.5″. Although it is related to the outside diameter, it is significantly different. Pipe is usually measured by NOMINAL PIPE SIZE (NPS). Refer to the table below to see the thicknesses of hardwood lumber that is rough or surfaced.Tubing is measured by the OUTSIDE DIAMETER (O.D.), specified in inches (e.g., 1.250) or fraction of an inch (eg. For example, a 4/4 board is 1″ thick when it’s purchased rough, but is 7/8″ thick after surfacing one side and is 13/16″ thick after surfacing two sides. ![]() These designations are important since they impact the actual thickness of a board. Boards that have been surfaced are referred to using the designations S1S, S2S, S3S, or S4S, depending on how many surfaces have been planed or sawn. To make things more confusing, hardwood lumber is also sold either rough-sawn or given a rough, finish surface on one, two, three, or all four sides. For example, a 1″ thick board is referred to as 4/4. Quarters refer to the number of quarters of an inch of board thickness. Hardwood lumber is often sized by the thickness of the board, which is measured in quarters rather than inches. Calculating board feet can be a little tricky, but it’s essentially just a measurement of the volume of the board.Ī board foot is equal to 144 cubic inches, or a board that measures 12″ long by 12″ wide by 1″ thick. 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?
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