October 14, 2022

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

A prism is a crucial figure in geometry. The figure’s name is originated from the fact that it is made by considering a polygonal base and stretching its sides until it cross the opposing base.

This blog post will take you through what a prism is, its definition, different kinds, and the formulas for volume and surface area. We will also give examples of how to use the information given.

What Is a Prism?

A prism is a 3D geometric shape with two congruent and parallel faces, well-known as bases, which take the shape of a plane figure. The other faces are rectangles, and their count rests 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 would be five sides.


The characteristics of a prism are interesting. The base and top each have an edge in common with the additional two sides, creating 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 parts:

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

  2. Two parallel planes which constitute of each base

  3. An fictitious line standing upright across any given point on any side of this figure's core/midline—usually 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 major kinds of prisms:

  • Rectangular prism

  • Triangular prism

  • Pentagonal prism

The rectangular prism is a regular type of prism. It has six faces that are all rectangles. It resembles a box.

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

The pentagonal prism has two pentagonal bases and five rectangular faces. It looks a lot like a triangular prism, but the pentagonal shape of the base stands out.

The Formula for the Volume of a Prism

Volume is a calculation of the total amount of space that an item occupies. As an crucial shape 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, where,

V = Volume

B = Base area

h= Height

Consequently, considering bases can have all kinds of figures, you will need to learn few formulas to figure out the surface area of the base. However, we will touch upon that later.

The Derivation of the Formula

To derive the formula for the volume of a rectangular prism, we need to look at a cube. A cube is a three-dimensional object with six sides 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 have a slice out of our cube that is h units thick. This slice will create 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 implies the height, which 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 type of prism.

Examples of How to Use the Formula

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

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 try another problem, let’s figure out 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 possess the surface area and height, you will figure out the volume without any issue.

The Surface Area of a Prism

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

There are a few distinctive methods to figure out the surface area of a prism. To figure out the surface area of a rectangular prism, you can use 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 calculate the surface area of a triangular prism, we will utilize 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 Finding the Surface Area of a Rectangular Prism

Initially, we will work on the total surface area of a rectangular prism with the following dimensions.

l=8 in

b=5 in

h=7 in

To calculate this, we will replace these values 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 Finding the Surface Area of a Triangular Prism

To calculate the surface area of a triangular prism, we will figure out the total surface area by ensuing similar steps as earlier.

This prism consists of 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 simple it is!

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