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What is the Size of the Interior Angle of a Regular 12-Sided Polygon?

What is the Size of the Interior Angle of a Regular 12-Sided Polygon?


Geometry is a fundamental branch of Maths that provides a deep understanding of objects and space's properties, shapes, and sizes. Polygons, with their equal sides and angles, are some of the most basic shapes in geometry, playing a critical role in applications from architecture to engineering and computer graphics.

In this blog, we will explore the interior angles of a polygon, specifically focusing on a regular twelve-sided figure, also known as a dodecagon, and how to calculate its aspects, including area, perimeter, and sum of angles, step by step. So, let's dive in!

Definition of a Twelve-sided Polygon

A dodecagon is a plane figure with 12 equal-length sides and 12 identical interior angles, bordered by straight sides.

To calculate the interior angles of a dodecagon, we use a general formula applicable to any polygon.

Application of the General Formula for Interior Angles

The general formula to determine the measure of any polygon's interior is:


where n is the number of sides. 

For a dodecagon, n = 12, and the formula becomes 

[(12−2)×180]12 = 150 degrees.

Step-by-Step Calculation for a Dodecagon

To calculate the size of the interior angle of a dodecagon, follow these steps:

1) Identify the number of sides (n = 12).

2) Substitute n into the general formula 

  • [(n−2)×180]n

  • [(12−2)×180]12

3) Simplify the formula to obtain the measure, which is 150 degrees.

[(10)×180]12 =  [1800]12 = 150

Simplifying the Calculation Process by Breaking Down the Polygon

Breaking down the twelve-sided polygon into smaller shapes offers an alternative method for calculating the interior measures.

For instance, dividing the dodecagon into twelve triangles, each with a vertex at the centre, allows us to calculate the sum of the interior measures of these triangles and then divide by twelve to find each measure.

The diagonals formed in the process can be used to better understand the structure and area of the dodecagon. Each diagonal helps in forming these triangles, making the calculation of area and perimeter more manageable.

Additionally, the patterns formed by these diagonals offer insights into the geometric properties of the dodecagon.

Significance: Practical Applications and Examples

The interior measures of regular polygons have many practical applications, particularly in art, design, and construction. For example, architects utilise these measurements to design regular shapes for structures like windows, doors, and roofs.

In graphic design, regular polygons are employed to create 2D shapes, fonts, and logos. Furthermore, these measurements are crucial in computing, especially for 3D modelling, rendering, and simulation algorithms. 

Addressing Common Misconceptions

Finding the size of the interior angles of a polygon might seem challenging at first, but it is not as complicated as many students think. Some common misconceptions in angle calculation include confusing the formulas for interior and exterior angles, mixing up the number of sides with the number of angles, and forgetting to divide by the number of angles. 

Therefore, it is crucial to understand the concepts and practice solving many exercises to avoid such mistakes.

Alternative Methods for Finding Interior Angles

Apart from the general formula, other methods for determining the measurements of polygonal corners include the diagonal method, the apothem method, and the exterior angle method. These techniques involve drawing additional lines inside or outside the shape to create new shapes for calculating these measurements.


In conclusion, calculating the angle of a dodecagon is straightforward, either by using the general formula or by breaking down the polygon into simpler shapes, focusing on each vertex and the patterns formed by the diagonals. Understanding these concepts is vital in a broad range of applications, from simple geometric calculations to more complex architectural designs.

Author: MyEdSpace
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