A scale factor represents the ratio of two corresponding lengths in similar geometric shapes. Two shapes must be similar for the scale factor between the two of them to be a relevant ratio. To compute the scale factor, one should divide the length of one shape's side by the corresponding length of the other shape's side.
Scale factors are used as ratios to compare shapes in one, two or three dimensions, according to I Coach Math. For example, calculating scale factor applies to lines, polygons and volume figures. The scale factor from the larger shape to the smaller shape is a ratio between zero and one; when multiplying lengths of the larger shape by the scale factor, the smaller shape is formed. Squaring the scale factor results in the ratio of areas between two similar two-dimensional shapes. Similarly, cubing the scale factor results in the ratio of volumes of similar three-dimensional shapes.