For uniformity in lumber sizes and qualities, certain general rules are adopted by lumber producers, who adopt, also, specific rules for the inspection of each kind of wood according to its uses. Lumber rules are subject to changes particularly because of the increasing scarcity of wood.

(1) Standard lumber lengths are 6, 8, 10, 12, 14, and 16 feet, though 6- and 8-foot lengths are for special uses. Boards measuring an odd number of feet are classed with the next lower even lengths, unless specified otherwise.

(2) Standard thicknesses are 3/8, 1/2, 5/8, 3/4, 1, 1 1/4, 1 1/2, 2, 2 1/2, 3, and 4 inches. Pieces larger than 4 x 4 inches are called timbers.

(3) The standard qualities or grades for hardwoods are, usually, firsts, seconds, and one or more grades of common. Soft woods are graded according to their uses. An inspector determines the grade to which any piece of lumber belongs by its width, amount of heart or sap, and defects affecting its strength and appearance.

(4) Inspection is usually made of the worst side of the board, and warps are always considered as defects.

It is not uncommon for purchasers of large amounts of lumber to have their own specifications for the general inspection of lumber.