Every 3D solid is built from three kinds of part. A face is a flat surface you could paint. An edge is the straight line where two faces meet. A vertex is a corner point where edges meet (the plural is vertices). A cube, for example, has 6 faces, 12 edges and 8 vertices. Count one kind at a time — trace every line for edges, poke every corner for vertices — and remember the parts you cannot see behind the solid still count.
Explore this idea with maths tools
Maths you can move
Build 8 + 5
Tap two gold counters to fill the ten-frame.
8 in the frame + 5 waiting. The total stays the same.
Words to know
- face
- a flat surface of a solid
- edge
- the line where two faces meet
- vertex
- a corner point where edges meet
Worked examples
How many faces does a cube have?
- 1.A cube has 6 flat sides.
- 2.Count them all, including the hidden 3.
= 6
How many edges does a triangular prism have?
- 1.Trace each line where two faces meet.
- 2.There are 9 edges.
= 9
How many vertices does a square pyramid have?
- 1.Poke each corner point.
- 2.4 around the base and 1 at the top makes 5.
= 5
For parents
Method: Handle a real solid and count one part at a time.
What to say: Ask them to colour the flat faces, trace the edges with a finger, then poke the corners.
Common mistakes:
- Swapping edges and faces (a cube: saying 6 edges).
- Counting only the faces they can see and forgetting the hidden ones.