October 14, 2022

Volume of a Prism - Formula, Derivation, Definition, Examples

A prism is an important figure in geometry. The shape’s name is originated from the fact that it is created by taking into account a polygonal base and expanding its sides till it cross the opposing base.

This blog post will discuss what a prism is, its definition, different types, and the formulas for volume and surface area. We will also provide instances of how to utilize the data given.

What Is a Prism?

A prism is a 3D geometric shape with two congruent and parallel faces, called bases, that take the form of a plane figure. The additional faces are rectangles, and their count relies on how many sides the identical base has. For instance, if the bases are triangular, the prism would have three sides. If the bases are pentagons, there will be five sides.


The characteristics of a prism are fascinating. The base and top both have an edge in parallel with the additional two sides, making them congruent to one another as well! This means that all three dimensions - length and width in front and depth to the back - can be deconstructed into these four entities:

  1. A lateral face (meaning both height AND depth)

  2. Two parallel planes which constitute of each base

  3. An illusory line standing upright across any given point on either side of this figure's core/midline—also known collectively as an axis of symmetry

  4. Two vertices (the plural of vertex) where any three planes meet

Kinds of Prisms

There are three primary kinds of prisms:

  • Rectangular prism

  • Triangular prism

  • Pentagonal prism

The rectangular prism is a common type of prism. It has six faces that are all rectangles. It matches the looks of a box.

The triangular prism has two triangular bases and three rectangular faces.

The pentagonal prism consists of two pentagonal bases and five rectangular sides. It seems a lot like a triangular prism, but the pentagonal shape of the base makes it apart.

The Formula for the Volume of a Prism

Volume is a measurement of the total amount of area that an thing occupies. As an important shape in geometry, the volume of a prism is very relevant in your learning.

The formula for the volume of a rectangular prism is V=B*h, where,

V = Volume

B = Base area

h= Height

Finally, considering bases can have all sorts of shapes, you will need to know a few formulas to determine the surface area of the base. However, we will go through that later.

The Derivation of the Formula

To extract the formula for the volume of a rectangular prism, we are required to look at a cube. A cube is a three-dimensional item with six faces that are all squares. The formula for the volume of a cube is V=s^3, assuming,

V = Volume

s = Side length

Now, we will take a slice out of our cube that is h units thick. This slice will by itself be a rectangular prism. The volume of this rectangular prism is B*h. The B in the formula stands for the base area of the rectangle. The h in the formula implies the height, that is how thick our slice was.

Now that we have a formula for the volume of a rectangular prism, we can use it on any kind of prism.

Examples of How to Use the Formula

Considering we have the formulas for the volume of a triangular prism, rectangular prism, and pentagonal prism, let’s put them to use.

First, let’s figure out the volume of a rectangular prism with a base area of 36 square inches and a height of 12 inches.



V=432 square inches

Now, let’s try one more problem, let’s calculate the volume of a triangular prism with a base area of 30 square inches and a height of 15 inches.



V=450 cubic inches

As long as you have the surface area and height, you will calculate the volume with no issue.

The Surface Area of a Prism

Now, let’s discuss about the surface area. The surface area of an object is the measurement of the total area that the object’s surface occupies. It is an crucial part of the formula; consequently, we must understand how to find it.

There are a few different ways to work out the surface area of a prism. To calculate the surface area of a rectangular prism, you can utilize this: A=2(lb + bh + lh), where,

l = Length of the rectangular prism

b = Breadth of the rectangular prism

h = Height of the rectangular prism

To figure out the surface area of a triangular prism, we will employ this formula:



b = The bottom edge of the base triangle,

h = height of said triangle,

l = length of the prism

S1, S2, and S3 = The three sides of the base triangle

bh = the total area of the two triangles, or [2 × (1/2 × bh)] = bh

We can also utilize SA = (Perimeter of the base × Length of the prism) + (2 × Base area)

Example for Calculating the Surface Area of a Rectangular Prism

First, we will figure out the total surface area of a rectangular prism with the following information.

l=8 in

b=5 in

h=7 in

To figure out this, we will replace these numbers into the respective formula as follows:

SA = 2(lb + bh + lh)

SA = 2(8*5 + 5*7 + 8*7)

SA = 2(40 + 35 + 56)

SA = 2 × 131

SA = 262 square inches

Example for Calculating the Surface Area of a Triangular Prism

To compute the surface area of a triangular prism, we will work on the total surface area by following similar steps as earlier.

This prism will have a base area of 60 square inches, a base perimeter of 40 inches, and a length of 7 inches. Therefore,

SA=(Perimeter of the base × Length of the prism) + (2 × Base Area)


SA = (40*7) + (2*60)

SA = 400 square inches

With this data, you will be able to work out any prism’s volume and surface area. Test it out for yourself and observe how easy it is!

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