Similar and Congruent Shapes

When you compare two or more shapes, they can be classified as similar or congruent:

  • Similar means they have the same shape but different size.
  • Congruent means they have the same shape and same size.

Examples of similar or congruent geometry shapes:

Congruent shapes have the same size angles, side lengths, area, and perimeter.

Similar shapes have related parts. Their angles are the same, and side lengths share the same proportions.

For example, if there are two similar triangles, they may both have angle measures of 90º, 30º, and 60º.

If the side lengths of one triangle were 3, 4, and 5, the side lengths of the second triangle would all have to be equally larger or smaller, meaning all twice as big, or three times as big. Here are some possible side lengths:

  • Triangle #1: 3, 4, 5
  • Triangle #2: 6, 8, 10 (two times the original)
  • 9, 12, 15 (three times the original)
  • 1.5, 2, 2.5 (0.5 times the original)