What is a line of symmetry?
A line of symmetry is a line that divides a figure into two parts that are mirror images of each other.
- A square has 4 lines of symmetry.
- A circle has many lines of symmetry (any line through the center).
- A heart shape has 1 line of symmetry (down the middle).
Each half must look exactly the same but flipped, like a reflection in a mirror.
How do you identify a line of symmetry?
To identify a line of symmetry, imagine folding the shape along a line. If the two halves match perfectly, the line is a line of symmetry.
- Draw or imagine a line across the shape.
- Fold the shape (mentally or on paper).
- If both sides fit exactly, that line is a line of symmetry.
Not every line drawn through a shape is a line of symmetry—only the ones where both sides match exactly.
Common shapes and their lines of symmetry
Many familiar shapes have predictable numbers of lines of symmetry. Knowing these can help you recognize symmetry quickly.
- Rectangle → 2 lines of symmetry
- Square → 4 lines of symmetry
- Equilateral triangle → 3 lines of symmetry
- Circle → many lines of symmetry
- Parallelogram → 0 lines of symmetry (in most cases)
Shapes may have zero, one, or many lines of symmetry. Be sure to test carefully.
Using symmetry in real life
Symmetry is not only in math—it appears in nature, art, and design. Recognizing symmetry can help you understand patterns and balance.
- A butterfly’s wings are symmetrical.
- A human face has approximate symmetry.
- Many buildings and designs use symmetry for balance and beauty.
When you see symmetry in the real world, think of it as nature or design using the same rule you use in geometry.