In calculating the sectional areas of wires, the diameter in inches corresponding to the number of the gauge of the wire must first be determined, and this can be got only from tables. Then to find the area of cross-section in square inches, square the diameter in inches (that is, multiply it by itself), and multiply by .7854. To find the weight in pounds of a single wire, multiply the cross-section, determined as just described, by the length in inches and by .28 for iron or by .31 for cupper. To determine approximately the weight in pounds of a stranded cable, multiply the weight of the length of single wire by the number of wires in the strand.