A three-dimensional (3D) object is solid rather than flat. It can be measured in three different directions: length, width and depth. Cubes, pyramids, spheres, cylinders and cones are all examples of 3D shapes.

Cubes and cuboids

A cube has 12 edges of equal length, 8 vertices, and its 6 faces are all the same length and width. Each face has a square shape.

A cuboid also has 12 edges and 8 vertices and 6 faces, but they have different lengths and widths. Each face has a rectangular shape.

Cones and cylinders

Cones have 2 faces: one flat, circular face on the bottom, and another on top that curves all the way around, forming a point. Where these two faces meet at the base, there is 1 edge. A cone has 1 vertex, at the pointed tip.

A cylinder looks like a tube, or a tin can. It has 3 faces: a circular face at each end and a curved face between them. These faces meet at the 2 edges. There are no vertices.

A square-based pyramid has 5 faces. One of the faces—the base—is a square, and the others are triangles of equal size. It has 8 edges and 5 vertices.

A triangular-based pyramid is known as a tetrahedron. Its 4 faces are all triangular. It has 6 edges and 4 vertices.

Spheres

A sphere is completely round. It has only one face: a curved face that goes all the way around it. It has no vertices, and no edges. A ball is an example of a sphere.

Prisms

The two ends of a prism are always the same shape and size. A triangular prism has 5 faces: two triangular (at each end) and three rectangular. It has 9 edges and 6 vertices. A hexagonal prism has hexagonal faces at both ends.

If you were to open out a 3D shape, such as a cube, and lay it flat, you would have a net.

A 3D shape can have more than one possible net.
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One of the best ways to understand nets is to cut them out of paper, then fold them up into 3D shapes.

Key words

3D three-dimensional. A 3D shape is a solid object that has a length, a width and a depth

dimension something that can be measured, like a length, width or depth

edge where two faces on a 3D shape meet

face a flat surface that makes up a 3D shape

net what a 3D shape would look like if it were folded out flat

prism a type of 3D shape which has the same shaped face at both ends

vertex the corner of a 3D shape

vertices plural of vertex: the corners of a 3D shape