October 14, 2022

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

A prism is a vital figure in geometry. The shape’s name is derived from the fact that it is made by considering a polygonal base and stretching 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 give examples of how to use the details provided.

What Is a Prism?

A prism is a three-dimensional geometric figure with two congruent and parallel faces, known as bases, which take the shape of a plane figure. The other faces are rectangles, and their amount depends on how many sides the identical base has. For example, 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 each have an edge in common with the other two sides, making them congruent to one another as well! This implies that every three dimensions - length and width in front and depth to the back - can be broken down into these four entities:

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

  2. Two parallel planes which make up each base

  3. An illusory line standing upright through any provided point on any side of this figure's core/midline—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 main types 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 comprises of two pentagonal bases and five rectangular sides. It looks almost like a triangular prism, but the pentagonal shape of the base sets it apart.

The Formula for the Volume of a Prism

Volume is a calculation of the sum of area that an item occupies. As an important figure in geometry, the volume of a prism is very important for your learning.

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

V = Volume

B = Base area

h= Height

Ultimately, given that bases can have all types of figures, you are required to retain few formulas to calculate the surface area of the base. Despite that, we will touch upon that later.

The Derivation of the Formula

To derive the formula for the volume of a rectangular prism, we have to observe a cube. A cube is a three-dimensional object 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

Right away, we will have 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 implies the base area of the rectangle. The h in the formula stands for height, which is how thick our slice was.

Now that we have a formula for the volume of a rectangular prism, we can generalize it to any type of prism.

Examples of How to Utilize the Formula

Now that we understand the formulas for the volume of a triangular prism, rectangular prism, and pentagonal prism, let’s utilize these now.

First, let’s work on 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 work on one more question, let’s work on the volume of a triangular prism with a base area of 30 square inches and a height of 15 inches.



V=450 cubic inches

Provided that you possess the surface area and height, you will calculate the volume with no problem.

The Surface Area of a Prism

Now, let’s talk regarding the surface area. The surface area of an item is the measure of the total area that the object’s surface consist of. It is an essential part of the formula; therefore, we must know how to calculate it.

There are a several varied methods to find the surface area of a prism. To calculate the surface area of a rectangular prism, you can employ 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 use 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 use SA = (Perimeter of the base × Length of the prism) + (2 × Base area)

Example for Computing the Surface Area of a Rectangular Prism

Initially, we will determine the total surface area of a rectangular prism with the ensuing information.

l=8 in

b=5 in

h=7 in

To calculate this, we will put these values into the corresponding 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 Computing the Surface Area of a Triangular Prism

To compute the surface area of a triangular prism, we will find the total surface area by ensuing identical steps as before.

This prism consists of a base area of 60 square inches, a base perimeter of 40 inches, and a length of 7 inches. Hence,

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


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

SA = 400 square inches

With this information, you should be able to figure out any prism’s volume and surface area. Test it out for yourself and see how easy it is!

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