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Weights and Measures: Board
Board Measure. - Lumber is sold at so much "per M," meaning per thousand feet B. M. or board measure. Board measure is used in measuring lumber sawed into boards, planks, joists, scantling, etc. The unit of board measure is the board foot, which is 1 foot long, 1 foot wide, and 1 inch thick, and hence is equal to of a cubic foot. Hence to find the number of board feet in a board or other piece of lumber having square edges and parallel sides, first find the surface of the board in square feet and multiply the product by the thickness in inches. Boards 1 inch in thickness or less are sold by the square foot, surface measure.
Thus a board 1 foot wide and 16 feet long, if 1 inch or less in thickness, would contain 16 square feet or 16 feet board measure. A board 18 feet long, 6 inches wide, and 1 inch or less thick would contain 18 X 1/2 foot B. M. or 9 feet B. M. A joist 12 feet X 6 inches X 2 inches contains 12 X 2 X feet B. M. or 12 feet B. M.
The width of a board that tapers uniformly is averaged by taking one half the sum of the two ends, or, in practice, by measuring across the middle. In practice the width of a board is reckoned to the next smaller half inch. Thus, a width of 6 inches is taken as 6 inches, and the width of 64 inches is taken as 6½ inches.
To Measure Inch Boards. - Multiply the length in feet by the width in inches, and divide the product by 12. The quotient will be the contents in feet. For lumber 14 inches thick, add to the quotient. If 1½ inches thick, add. If 12 inches thick, add . If 2 inches thick, divide by 6 instead of by 12. If 21 inches thick, add to the quotient and so on. If 3 inches thick, divide by 4. If 4 inches thick, divide by 3. Or to ascertain the contents (board measure) of timber, including scantling, joist, WEIGHTS AND MEASURES planks, sills, rafters, etc., multiply the width in inches by the thickness in inches, and that by the length in feet and divide the product by 12. The result will be the number of feet.
The measurement of round logs is intended to give the amount of lumber in board measure that can be sawed from them. Logs not over 15 feet in length are measured by means of a table stamped on calipers, the length and diameter of the small end being given. In the case of logs over 16 feet in length, the average diameter is taken. Or to measure round timber take the girth in inches at both the large and the small ends, add them, and divide by 2, which gives the mean girth. The square of of the mean girth multiplied by the length of the timber in feet will give the contents in cubic feet. This is the common practice based on the estimate that round timber when squared loses . The result gives of the actual contents, the remaining being allowed for waste in sawing.
Or, by another rule, subtract 4 from the diameter of the log in inches, multiply the square of the remainder by the length of the log in feet. These two rules should give approximately the same result. Or to find how many solid feet a round stick of timber, if of the same thickness throughout, will contain when squared, square half the diameter in inches, multiply by 2 and multiply this product by the length in feet. Finally, divide by 144; the result will be the contents of the squared timber in solid feet.
Or to find the number of feet in timber having the bark on, square of the circumference in inches and multiply the product by twice the length in feet. Then divide by 144.
Subtract To to 1 of the total, according to the thickness of the bark. As a general rule, to find the solid contents of sawn lumber multiply the depth in inches by the breadth in inches and multiply the product by the length in feet and divide by 144.