the standard pre-cut sizes allows carpenters and house framers to buy lumber without having to do as much cutting when they get it to the construction site. because structural lumber is heavily used in construction its often machine stress graded so that builders know the bending stress of the board.
lumber sizes and measurement. once planed the wood is considered "finished.". thus the nominal size of the lumber you purchase is different from the actual size. usually there is 1/2 inch difference in measurements over 2 inches and 1/4 inch in measurements less than 2 inches.
when using studs other dimensions of 2-by-4 and 2-by-6 lumber is used. standard lengths for these range from 8 feet up to 16 feet. these lengths are used for wall plating window and door framing and bracing. other lengths are available for unusual situations.
every piece of 2 in. x 6 in. x 10 ft. kiln-dried heat treated dimensional lumber meets the highest grading standards for strength and appearance. this high quality lumber is ideal for a wide range of structural and nonstructural applications including framing of houses barns sheds and commercial construction.
the nominal dimensions of unsurfaced or rough-sawn lumber are the same as the actual dimensions so a 4-by-6 rough-sawn beam is actually 4 inches thick by 6 inches wide.
1 dimension lumber 2 thick and less than 14 wide is required to be dry with a moisture content of 19% or less. heavy dimension lumber 2×14 and wider 2-1/2 thick by all widths and 3×3 and larger and timbers are not required to be dry unless specified.
standard dimensions of softwood construction lumber. the american softwood lumber standard defines dry as a moisture content of 19 percent or less with an average of 15 percent. for example a board that has a nominal thickness of 1 inch has a standard green thickness of 25/32 inch and a standard dry thickness of 3/4 inch.
board foot: rough sawn lumber is usually sold by the "board foot" bd. ft. . a board foot is equal to a piece of wood 12 inches long x 12 inches wide and 1 inch thick or 144 cubic inches. to figure the board foot measurement of a piece of wood multiply the length x width x thickness in inches then divide by 144.
the thing that i have found a bit challenging when determining which timber to use has been the sizing. below is what i have been substituting for the dimensional lumber sizes noted in plans i am live in adelaide australia. i just wanted to run these past others here to see what they thought are
common sizes: nominal vs. actual. the most common type of dimensional lumber is the 2x4 two-by-four . due to the thickness of the saw the 2 x 4 is not 2 inches wide and 4 inches deep but is 1.5 in × 3.5 in 38 mm × 89 mm . so a 2 x 4 is nominally two inches by four inches but is actually 1.5 inches by 3.5 inches. when we say
in modern lumber practices the boards are no longer exactly 2 x 4 inches when first cut but today's drying and planing methods still leave the board 1 1/2 inches thick and 3 1/2 inches wide. the old standard of calling this board a 2 x 4 still remains even though in today's lumber practices the board has never been 2 x 4 inches in size.
commercial lumber dimensions - american softwood lumber standards - nominal and actual sizes are indicated in the table below. subtract 1/4 inch for dimensions under 2 inches 51 mm subtract 1/2 inch for dimensions under 8 inches 200 mm subtract 3/4 inch for larger dimensions.
the minimum joist size is a 2-by-6 which may span up to 11 feet 7 inches without additional support if they are spaced just 12 inches apart. its easy to compare the cost of a 2-by-6 to the cost of a 2-by-8 or 2-by-10 and think that using 2-by-6 joists will save money. sometimes it will if the deck is small.
the old standard of calling this board a 2 x 4 still remains even though in today's lumber practices the board has never been 2 x 4 inches in size. the actual vs. nominal sizes for common sizes of dimension lumber:
lumber - comes most commonly in 2 inch 2x468101216 and 4 inch 4x44x6 varieties. plywood - almost always 4x8 feet drywall/plasterboard - various 4 foot varieties 4x81012 and sometimes 5 foot.
standard lumber thicknesses come in 1 2 4 6 and 8 inches. in general 1-inch and 2-inch thicknesses are used for boards while 4-inch thicknesses are used for posts and structural supports and 8-inch thicknesses are used in landscaping such as for retaining walls.
it is the size of the rough wood before it is milled to it's standardized size. for hardwoods the nominal sizes are rounded to the nearest 1/4" for softwood construction lumber it is the nearest inch.