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 taking a polygonal base and extending its sides till it creates an equilibrium with the opposing base.

This article post will discuss what a prism is, its definition, different types, and the formulas for surface areas and volumes. We will also offer examples of how to use the data given.

What Is a Prism?

A prism is a 3D geometric figure with two congruent and parallel faces, called bases, which take the form of a plane figure. The other faces are rectangles, and their number rests on how many sides the similar base has. For example, 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 astonishing. The base and top each have an edge in parallel with the other two sides, creating them congruent to each other as well! This means 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 constitute of each base

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

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

Kinds of Prisms

There are three primary types 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 comprises of two pentagonal bases and five rectangular faces. It appears 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 calculation of the total amount of area that an item occupies. As an essential 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

Finally, given that bases can have all types of shapes, you have to learn few formulas to determine the surface area of the base. However, we will go through that later.

The Derivation of the Formula

To obtain the formula for the volume of a rectangular prism, we need to observe a cube. A cube is a three-dimensional item 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

Right away, we will take 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, 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 know the formulas for the volume of a pentagonal prism, triangular prism, and rectangular prism, now let’s use them.

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, consider another 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 have the surface area and height, you will calculate the volume without any issue.

The Surface Area of a Prism

Now, let’s talk regarding the surface area. The surface area of an object is the measurement of the total area that the object’s surface consist of. It is an crucial part of the formula; thus, we must understand how to find it.

There are a several varied ways 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), assuming,

l = Length of the rectangular prism

b = Breadth of the rectangular prism

h = Height of the rectangular prism

To compute 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 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 determine 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 plug 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 Computing the Surface Area of a Triangular Prism

To calculate the surface area of a triangular prism, we will find the total surface area by ensuing 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. Hence,

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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