Lines of symmetry

Symmetry is when one side of a shape is a mirror image of the other side.

Lots of buildings and everyday objects use symmetry because it looks appealing to the human eye.

Watch the video below from BBC Bitesize KS2 Maths which shows the lines of symmetry on a square, triangle, rectangle and circle.

A 2D shape is symmetrical if a line can be drawn through it and either side is a reflection of the other. You would call this the line of symmetry.

If you put a mirror on this line, you would see the whole shape in the reflection. That’s why a line of symmetry is sometimes called the mirror line.

Sometimes you can fold a shape in half, and if it fits into itself perfectly with no overlaps you have found a line of symmetry. Some shapes have more than one line of symmetry.

Let's look at some 2D shapes and their lines of symmetry.

These are shapes that have all equal sides and equal angles.

The number of lines of symmetry in a regular polygon is always the same as the number of sides!

Take a look at these examples:

These are shapes that have sides and angles of different sizes. Some irregular polygons also have lines of symmetry.

Even though a circle isn’t a polygon, it is still a 2D shape. As long as the line of symmetry goes directly through the centre of the circle, it has unlimited lines of symmetry!

Watch the video below from CBBC to learn more about symmetrical shapes.

Label the shapes in this interactive activity with the correct number of lines of symmetry.

Test what you know about lines of symmetry with this quiz!