Calculating Lumber Quantities
Large quantities of lumber are normally ordered by the board foot. A board foot is equivalent to a piece of lumber that is 1 inch thick, 12 inch wide, and 1 foot long.
When calculating board feet, always make sure you use the nominal lumber dimensions.
The following formula is used to calculate board feet.
Board feet = number of pieces x thickness in inches x width in inches x length in feet ÷ 12
For example, 20 pieces of 2 x 6 lumber that are each 8 foot long equals 160 board feet.
20 X 2 x 6 x 8 = 1,920 = 160 board feet
Calculating the Amount of Sheet Materials
To calculate the amount of sheet materials such as plywood, particleboard, drywall, and sheathing you need, calculate the area to be covered (length x width = area). The area will always be the square of the values used (square feet, square inches, etc.).
For example, to figure the amount of plywood decking needed for a 20 foot by 41 foot roof:
20 X 41 = 820 square feet
A standard 4 by 8 foot sheet contains 32 square feet. Therefore, if you divide 820 by 32, it yields 25 5/8 sheet, which is then rounded to 26 sheets.
Trim and Moldings
Trim and moldings are priced by the lineal foot and are ordered by the dimension of the piece (for example, 150 foot of 1 inch quarter round molding).