Measuring and Drawing Angles

Measuring Angles

The size of an angle is usually measured in degrees (°). Think of a circle which is divided into 360 equal sectors. Each sector has a small angle at the center of the circle – the size of such angle is 1 degree (written: 1°). In other words, the size of an angle is a measure of how wide the angle is at the vertex bound by the two sides.

Given an angle ABC,

How do we measure the size of the angle? We can measure angles using an instrument known as a protractor.

What is a protractor?

A protractor is an instrument used to measure the size of angles. It is shaped like a semicircle (180°) or a full circle (360°).

The following diagram shows a semicircle protractor. Scroll down the page to learn how to use a protractor.

The semicircle protractor shown below has two scales:
The outer scale starts from 0˚ to180˚ going clockwise.
The inner scale starts from 0˚ to 180˚ going anti-clockwise.
There are small lines or numbers on the scale that indicate the measurement in degrees.

The flat edge of a semicircular protractor is called the baseline. It usually has a 0-degree marking on either end. It is used to align with one side of the angle.

Most protractors have a small hole or mark at their center. This is the vertex point, which you align with the corner of the angle you’re measuring.

How to measure an angle using a protractor

To measure angle ABC, we need to:

Step 1: Place the center point of the protractor on the vertex B.

Step 2: Adjust the base line of the protractor so that it is aligned with the line BC

Step 3: Read the value of angle ABC, from the inner scale.

We can also adjust the base line of the protractor so that it is aligned with the line AB and use the outer scale to measure the angle.

Key Points

1. Protractor Alignment:
   Always align the baseline of the protractor with one ray and the center mark with the vertex.
   
2. Reading the Scale:
   Use the correct scale on the protractor (inner or outer) based on the direction of the angle.
   

How to measure and draw angles using a protractor?

The following videos will show you how to measure and draw angles using a protractor.

Measuring and Drawing Angles
How to measure angles and draw angles using a protractor?

• Show Video Lesson

Learn Acute, Obtuse & Right Angles & Measure Angles with a Protractor

• Show Video Lesson

Activity Using A Protractor

Measuring Angles
Practice lining up and reading a protractor while you measure a set of angles in this fun learning activity. The angles may range from 0° to 180°.

Steps to Draw an Angle Using a Protractor

1. Draw a Baseline:
   Use a ruler to draw a straight line. This will serve as one side of the angle.
   
2. Mark the Vertex:
   Choose a point on the baseline to be the vertex (the point where the two sides of the angle meet).
   
3. Place the Protractor:
   Align the baseline of the protractor with the baseline you drew.
   Ensure the center mark of the protractor is exactly at the vertex.
   
4. Mark the Angle:
   Locate the desired angle measurement on the protractor’s scale.
   Make a small mark at the corresponding degree on the paper.
   
5. Draw the Second Side:
   Use a ruler to draw a straight line from the vertex through the mark you made. This is the second side of the angle.
   6.Label the Angle:
   Optionally, label the angle with its measurement.
   

Key Points

1. Align the Protractor Correctly:
   Ensure the baseline of the protractor aligns with the baseline you drew, and the center mark is at the vertex.
   
2. Use the Correct Scale:
   Use the inner or outer scale on the protractor based on the direction of the angle.
   
3. Draw Accurately:
   Use a ruler to draw straight lines and ensure the angle is precise.
   
4. Label the Angle:
   Labeling the angle helps in identifying its measurement.
   

Try the free Mathway calculator and problem solver below to practice various math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.

We welcome your feedback, comments and questions about this site or page. Please submit your feedback or enquiries via our Feedback page.