Naming 2D Shapes

Counting sides and corners

A 2D shape is a flat shape — you can draw it on paper. We give it a name by counting two things: its sides (the straight edges) and its vertices (the corners, where two sides meet).

a triangle has 3 sides and 3 corners;
a quadrilateral has 4 sides — a square and a rectangle are both quadrilaterals;
a pentagon has 5 sides;
a hexagon has 6 sides;
an octagon has 8 sides;
a circle has no straight sides at all — it is one smooth curve.

A flat shape made only of straight sides is called a polygon. So a triangle, a square, a pentagon, a hexagon and an octagon are all polygons — but a circle is not.

The rule for naming polygons

Notice the handy pattern: for a polygon, the number of corners is always the same as the number of sides. So once you can count the sides, you know the name.

for any polygon, the number of sides equals the number of vertices (corners);
counting sides gives the name: triangle 3, quadrilateral 4, pentagon 5, hexagon 6, heptagon 7, octagon 8;
a regular shape has all its sides and all its angles equal (a regular quadrilateral is a square);
a circle is a curve, not a polygon — it has no straight sides and no corners.

The shape gallery

Step through the gallery to meet one shape at a time. Each is labelled with its name and how many sides it has — count the corners and you will get the same number, except for the circle.