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Naming Circles, Squares, and Triangles · Shape and Pattern · CCSS.MATH.CONTENT.K.G.A.2 · 2D shapes

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Naming Circles, Squares, and Triangles

with Lumi

Lumi sits on a colorful classroom rug covered with big and small wooden shape tiles — triangles, squares, and circles — in many colors, holding up a tiny red triangle and a huge yellow triangle side by side with a big smile, while a blue circle and an orange square rest on the rug nearby.

Identify a circle, square, and triangle by counting their sides and corners.
Recognize that shape names do not change when size or color changes.
Identify that a shape keeps its name when it is turned or flipped.
Compare two shapes and say how many sides each one has.
Sort a group of shapes by name using sides and corners as clues.

Key terms

side: A straight edge that forms the outside of a shape.
corner: The point where two sides of a shape meet.
triangle: A flat shape with exactly three sides and three corners.
square: A flat shape with four equal sides and four corners.
circle: A round flat shape with no sides and no corners.

Count Sides and Corners

The best way to name a flat shape is to count its straight sides and its corners. A triangle has three sides and three corners, a square has four sides and four corners, and a circle has none of either because it is perfectly round. The number of sides is the surest clue, so when you are unsure, just count carefully around the whole shape.

Size, Color, and Turning

A shape keeps its name no matter how big or small it is or what color it is, because the name comes only from the sides and corners. Turning a shape or flipping it upside down does not add or remove any sides either. A tiny red triangle and a huge blue triangle are both triangles, and a tilted square is still a square.

Worked examples

Name a shape with 3 sides and 3 corners.

Count the sides: 1, 2, 3.
Three sides and three corners match a triangle.
Size and color do not change the name.

Answer: triangle

Is a tilted four-equal-sided shape still a square?

Count the sides: 1, 2, 3, 4.
All four sides are the same length.
Turning it does not change the sides.

Answer: Yes, it is still a square.

Hi, I am Lumi! Look at the shapes I have. This is a triangle. Count the sides with me: 1, 2, 3. A triangle always has 3 sides and 3 corners. It does not matter if it is big or tiny. It does not matter if it is red or blue. Three sides means triangle! This is a square. Count the sides: 1, 2, 3, 4. A square has 4 sides and 4 corners, and all the sides are the same length — that is what makes it a square and not just any 4-sided shape. This is a circle. A circle has NO sides and NO corners. It is perfectly round all the way around. Here is the big idea: we name a shape by counting its sides and corners — not by its size or its color. A huge green triangle and a tiny orange triangle have the same name because they both have 3 sides and 3 corners. A big blue circle and a small red circle are both still circles! Now here is one more thing. Even if I turn a triangle on its side or tip it upside down, it is STILL a triangle! The same is true for a square — spin it and it is still a square. A circle looks the same no matter how you turn it! Spinning or flipping a shape does not change how many sides it has. Count the sides — and you will always know the name! Not sure? Just count the sides. That will always tell you the name!

Activity

Drag each shape into the box that matches its name.

Practice

Look at a round shape with no corners and name it correctly.

Sort shapes into triangles, squares, and circles by counting sides.

Common mistakes to avoid

Bigger shapes get new namesSize never changes a shape's name; a big triangle and a small triangle are both triangles.
Turning a shape changes its sidesFlipping or rotating a shape keeps the same number of sides, so the name stays exactly the same.

Check your understanding

Lumi holds a big green shape with 3 sides and 3 corners. What is the name of this shape?

A tiny orange square and a huge orange square — do they have the same name?

Which shape has NO sides and NO corners?

Lumi tips a triangle upside down. Now how many sides does it have?

What makes a square different from a rectangle, which also has 4 sides and 4 corners?

Recap

We name flat shapes by counting their sides and corners, not by size or color. A triangle has three sides, a square has four equal sides, and a circle has none. Turning or flipping a shape never changes its name.

Reflect

What shapes can you find around your home, and how do you know their names?