Lines of symmetry
A line of symmetry is a line through a shape such that folding along the line would make the two halves match exactly.
How to find one
- Imagine folding the shape in half along a line.
- If both halves overlap perfectly, that line is a line of symmetry.
- If they don't, it's not.
How many lines does a shape have?
| Shape | Lines of symmetry |
| Square | 4 |
| Rectangle | 2 |
| Equilateral triangle | 3 |
| Isosceles triangle | 1 |
| Scalene triangle | 0 |
| Circle | infinite |
| Regular pentagon | 5 |
| Regular hexagon | 6 |
A regular polygon (all sides and angles equal) has as many lines of symmetry as it has sides.
Where the lines are
For a square, the 4 lines run:
- vertically (top to bottom),
- horizontally (left to right),
- corner to corner (both diagonals).
For a rectangle, the 2 lines run vertically and horizontally through the centre — but not diagonally, because the diagonal halves wouldn't overlap (the rectangle isn't square).
Real-life symmetry
- Most letters of the alphabet — A, H, I, M, O, T, U, V, W, X, Y — have at least one line of symmetry.
- Butterflies have 1 line (down the middle of the body).
- Most leaves have 1.
Try it
- 🪞 Symmetry
Summary
- Line of symmetry = imaginary fold line where halves match exactly.
- A regular polygon has the same number of lines of symmetry as sides.
- Square: 4. Rectangle: 2. Equilateral triangle: 3. Circle: infinite.