Definition of scale factor

A scale factor is the ratio of sizes of two similar figures. For example, the scale factor is 2 for the following two similar figures.

Scale factor of 2

The scale factor is 2 because the triangle on the right is two times bigger than the triangle on the left.


How to find the scale factor

  1. Decide which figure is the original figure.

  2. Make a ratio of corresponding sides. Scale factor is equal new figure divided by original figure.

      3.Simplify, if possible.

For the two similar figures above, the original figure is the triangle on the left.

A ratio of corresponding sides is equal to 16/8 or 2.

If on the other hand, we make the triangle on the right our original figure, the scale factor is 8/16 or 1/2.




If the triangles are not similar, then you cannot find the scale factor

When two figures are identical in size, the scale factor is equal to 1.

When a figure is shrunk, the scale factor is less than 1.

When a figure is enlarged, the scale factor is bigger than 1.

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