October 14, 2022

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

A prism is an important figure in geometry. The figure’s name is originated from the fact that it is created by taking into account a polygonal base and extending its sides as far as it intersects the opposite base.

This article post will take you through what a prism is, its definition, different types, and the formulas for surface areas and volumes. We will also offer instances of how to employ the data given.

What Is a Prism?

A prism is a three-dimensional geometric figure with two congruent and parallel faces, called bases, which take the form of a plane figure. The additional faces are rectangles, and their amount depends 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 properties of a prism are fascinating. The base and top both have an edge in common with the additional 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 parts:

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

  2. Two parallel planes which constitute of each base

  3. An imaginary line standing upright through any given 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 join

Types of Prisms

There are three major kinds of prisms:

  • Rectangular prism

  • Triangular prism

  • Pentagonal prism

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

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

The pentagonal prism has two pentagonal bases and five rectangular sides. It seems 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 studies.

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

V = Volume

B = Base area

h= Height

Ultimately, given that bases can have all sorts of shapes, you have to know a few formulas to determine the surface area of the base. Despite that, we will go through that afterwards.

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 3D 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

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 dense 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 Use the Formula

Since we have 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 one more question, 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

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

The Surface Area of a Prism

Now, let’s talk about the surface area. The surface area of an object 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 find it.

There are a few different ways to figure out the surface area of a prism. To measure 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 work 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 Computing the Surface Area of a Rectangular Prism

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

l=8 in

b=5 in

h=7 in

To calculate this, we will put these numbers 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 find the surface area of a triangular prism, we will work on the total surface area by following identical steps as priorly used.

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

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


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

SA = 400 square inches

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

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