Prisms

Go to Surface Area or Volume.

pentagonal prism

A prism is a solid object with:

 

A cross section is the shape made by cutting straight across an object.

prism cross section

The cross section of this object is a triangle ...

.. it has the same cross section all along its length ...

... so it's a triangular prism.


Try drawing a shape on a piece of
paper (using straight lines)

Then imagine it extending up from the sheet of paper ...
... that's a prism !

Drawing a Prism

Prism not cylinder

No Curves!

A prism is a polyhedron, which means all faces are flat!

No curved sides.

For example, a cylinder is not a prism, because it has curved sides.

Bases

bases
The ends of a prism are parallel
and each one is called a base.

Sides

prism sides
The side faces of a prism are parallelograms
(4-sided shapes with opposite sides parallel)

These are all Prisms:


Square Prism: Cross-Section:
cuboid square

Cube: Cross-Section:
cube square
(yes, a cube is a prism, because it is a square
all along its length)
(Also see Rectangular Prisms )

Triangular Prism: Cross-Section:
triangular prism triangle

Pentagonal Prism: Cross-Section:

pentagonal prism
pentagon

and more!

Regular and Irregular Prisms

All the previous examples are Regular Prisms, because the cross section is regular (in other words it is a shape with equal edge lengths, and equal angles.)

Here is an example of an Irregular Prism:

Irregular Pentagonal Prism:    

irregular pentagonal prism
  irregular pentagon
  Cross-Section
It is "irregular" because the
cross-section is not "regular" in shape.

Surface Area of a Prism

prism area of base, perimeter of base and length

 

Surface Area =   2 × Base Area
  +  Base Perimeter × Length

Example: What is the surface area of a prism where the base area is 25 m2, the base perimeter is 24 m, and the length is 12 m:

 

Surface Area   = 2 × Base Area + Base Perimeter × Length
    = 2 × 25 m2 + 24 m × 12 m
    = 50 m2 + 288 m2
    = 338 m2

 

(Note: we have an Area Calculation Tool)

Volume of a Prism

The Volume of a prism is the area of one end times the length of the prism.

prism area of base, perimeter of base and length

Volume = Base Area × Length

Example: What is the volume of a prism where the base area is 25 m2 and which is 12 m long:

Volume   = Area × Length
    = 25 m2 × 12 m
    = 300 m3

More About The Side Faces

prism sides

The side faces of a prism are parallelograms (4-sided shape with opposites sides parallel)

 

A prism can lean to one side, making it an oblique prism, but the two ends are still parallel, and the side faces are still parallelograms!

 

But if the two ends are not parallel it is not a prism.