The first thing to know in determining the size of beam or timber is the weight or force load the timber is to support and the location of the load.

Very careful experiments have been made in testing laboratories (Fig. 102) to determine the tensile or pulling strength of materials under different conditions. The results of these experiments have been compiled and published in tabular form, as shown below. Mechanics and contractors can find the strength of any material of any size by looking in the table.