Maths topic

2D shapes

2D shapes are flat shapes. We can name them by looking carefully at their sides, vertices, curves and special properties.

Practise quadrilaterals Explore shapes Back to topics

the big idea

A shape name is a clue. Count the sides and vertices, check whether the boundary is straight or curved, and look for special properties.

name triangle, square, circle
count sides and vertices
properties equal, parallel, right angles

choose a shape

Pick a 2D shape and read its important properties.

triangle

triangle

sides3 sides vertices3 vertices featureclosed polygon

closed polygon

what is a 2D shape?

A 2D shape is flat. It has length and width, but it is not a solid object.

  • 2D means two-dimensional.
  • A 2D shape can have straight sides, a curved boundary or both.
  • The boundary is the outside line around the shape.
length width
flat length and width

common 2D shape names

Some shape names are learned by matching the drawing and the properties.

  • A circle has one curved boundary and no vertices.
  • A triangle has 3 straight sides and 3 vertices.
  • A square and a rectangle both have 4 straight sides and 4 vertices.
  • Pentagon, hexagon and octagon names tell us how many sides the shape has.
circle 0 straight sides 0 vertices

one curved boundary

oval 0 straight sides 0 vertices

one stretched curved boundary

triangle 3 sides 3 vertices

closed polygon

square 4 equal sides 4 vertices

4 right angles

rectangle 4 sides 4 vertices

opposite sides equal and 4 right angles

pentagon 5 sides 5 vertices

closed polygon

hexagon 6 sides 6 vertices

closed polygon

octagon 8 sides 8 vertices

closed polygon

counting properties

Properties are features we can notice and describe. Counting sides and vertices helps us name many shapes.

  • Sides are straight parts of the boundary.
  • Vertices are corner points where straight sides meet.
  • Curved shapes do not have straight sides at the curved part.
  • Use the properties to check the name, not just how the shape is turned.
shape sides vertices feature
circle 0 straight sides 0 vertices curved boundary
triangle 3 sides 3 vertices 3 sides
square 4 equal sides 4 vertices 4 equal sides
rectangle 4 sides 4 vertices 4 sides
pentagon 5 sides 5 vertices 5 sides
hexagon 6 sides 6 vertices 6 sides
octagon 8 sides 8 vertices 8 sides

polygons

A polygon is a closed 2D shape made only from straight sides.

  • Triangles, squares, rectangles, pentagons, hexagons and octagons are polygons.
  • Circles and ovals are not polygons because their boundary is curved.
  • A polygon must be closed. The sides join all the way around.
polygons
triangle pentagon hexagon
closed with straight sides
not polygons
circle oval
curved boundaries

quadrilaterals

A quadrilateral is any closed 2D shape with 4 straight sides.

  • A square has 4 equal sides and 4 right angles.
  • A rectangle has opposite sides equal and 4 right angles.
  • A rhombus has 4 equal sides.
  • A parallelogram has opposite sides parallel.
  • A trapezium has one pair of parallel sides.
  • A kite has two pairs of touching equal sides.
square 4 equal sides 4 vertices

4 right angles

rectangle opposite sides equal 4 vertices

4 right angles

rhombus 4 equal sides 4 vertices

opposite sides parallel

parallelogram opposite sides equal 4 vertices

opposite sides parallel

trapezium 4 sides 4 vertices

one pair of parallel sides

kite two pairs of equal touching sides 4 vertices

4 straight sides

shapes can belong to groups

Some shapes fit inside bigger groups. A square is a square, but it is also a quadrilateral because it has 4 straight sides.

  • A triangle is a polygon because it is closed and has straight sides.
  • A rectangle is a quadrilateral because it has 4 straight sides.
  • A square is also a rectangle when we use the property of 4 right angles and opposite sides equal.
  • When you are not sure, check the properties one at a time.
polygons
quadrilaterals
rectangles
square

A square is inside these groups because its properties fit each group.

property words

Property words help us describe and sort 2D shapes.

1 side straight part

one straight part of the boundary

2 vertex corner

where two straight sides meet

3 curve curved part

a boundary that bends instead of staying straight

4 parallel same direction

lines or sides that never meet

5 right angle square corner

a 90 degree corner

6 equal sides same length

sides that match in length

shape facts

triangle 3 sides
quadrilateral 4 sides
pentagon 5 sides
hexagon 6 sides
octagon 8 sides
circle curved boundary

real world examples

signs stop signs use octagons
tiles floors can use squares, rectangles or hexagons
screens tablets and boards are rectangles
wheels wheels and clocks use circles
patterns fabric, art and games use repeated shapes
maps parks, courts and rooms can be drawn as 2D shapes

quick shape quiz

Try a few shape ideas. This quiz only asks about ideas shown on this page.

Which 2D shape has 3 straight sides?

What do we call a corner point where sides meet?

Which shape is not a polygon?

How many straight sides does a quadrilateral have?

Which property does a square have?