180 degree angle

180 degree angle
Go back to  'Angles'

In this mini-lesson, we will learn about 180-degree angles. While doing so we will also discuss creating a 180-degree angle with a compass, and steps to be followed to construct a 180-degree angle. You can check out the interactive simulations to know more about the lesson and try your hand at solving a few interesting practice questions at the end of the page.

Before we get started, have you ever noticed the angle between the two hands of a clock when at 6 o'clock?

180 degree real life example

The angle between the two hands of the clock above is 180° because it forms a straight line.

Let us explore more about the 180° angle.

Lesson Plan 


What Is 180 Degree Angle?

We know that an angle is formed when two rays meet at a vertex. 

vertex definition maths

If the angle formed at the vertex O measures 180°, we call it a 180-degree angle.

A straight angle is called a 180-degree angle. 

It is also called a half-circle. It looks like a straight line. 

type of straight angle

How to Construct 180-Degree Angle Using a Protractor?

In this section, let us explore how to construct a 180-degree angle with the help of a protractor.

Follow the given steps:

  • Step 1: Draw a line segment \(OA\)
  • Step 2: Place the protractor at the point \(O\)
  • Step 3: In the outer circle of the protractor look for 180° reading and with a pencil mark a dot and name it \(C\)
  • Step 4: Join \(O\) and \(C\). Now,  \(\angle AOC =180 ^\circ\)

Still, confused? Look at the simulation below.

Click on the "Go" button to understand the process of construction of a 180-degree angle using a protractor.

What Are 180-degree Angles in Real Life?

180° angles are widely seen in real life.

In everyday life, 180-degree angles are used. For constructing structures, highways, houses, and sports facilities, engineers and architects use angles. Carpenters make benches, tables, and sofas using angles.

180 degree example

Observe where you can see 180° angles in your surrounding areas.

Thinking out of the box
Think Tank
  • How many 180-degree angles are there in a complete angle?

Solved Examples

Example 1



Can you help Alex find out the difference between a 180° angle and a 90° angle?


The 180-degree angle is a straight line, known as a semi-circle.

A 90-degree angle is a quadrant or one-fourth of a circle.

180-degree is a straight line or semicircle and 90 degree is a quadrant
Example 2



Alina wants to construct a 180° angle using a protractor. Can you help her construct?


Step 1: Draw a ray (part of a line that has a vertex at one end and an arrowhead at another). Mark the vertex as point O.

Step 2: Point O denotes the vertex of the angle.

Step 3: Now put the protractor above the point O vertex and match the baseline of the protractor along with the arm of the angle.

Step 4: Mark the angle 180 degrees with a dot.

Step 5: Now join this new vertex with point O. This forms another arm of the angle.

Now, we get a straight angle.

type of straight angle

important notes to remember
Important Notes
  1. The 180-degree angle is also called a straight angle, half-circle, or semi-circle.
  2. A 180-degree angle can be constructed with a protractor or a compass.

Interactive Questions 

Here are a few activities for you to practice. Select/Type your answer and click the "Check Answer" button to see the result.


Let's Summarize

We hope you enjoyed learning about a 180-degree angle with the simulations and practice questions. Now, you will be able to easily solve problems on a 180-degree angle triangle, constructing a 180-degree angle with a compass, and other related applications of a 180-degree angle.

About Cuemath

At Cuemath, our team of math experts is dedicated to making learning fun for our favorite readers, the students!

Through an interactive and engaging learning-teaching-learning approach, the teachers explore all angles of a topic.

Be it worksheets, online classes, doubt sessions, or any other form of relation, it’s the logical thinking and smart learning approach that we, at Cuemath, believe in.

FAQs on the 180-degree angle

1. What does a 180-degree angle look like?

A 180 degree looks like a straight line.

2. How do you find an angle without a protractor?

An angle can be found out without a protractor by using a compass or slope form.

3. How many 180-degree angles does it take to make a full turn?

It takes two 180-degree angles to make a full turn.

4. What type of angle is a 180-degree angle?

The 180-degree angle is a straight angle because it forms a straight line.

5. Is a 180-degree angle obtuse?

An obtuse angle measures more than 90° but less than 180°, therefore, 180 degree angle is not an obtuse angle.

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