Lesson 19 — Activity 2: Measuring Angles


There are different ways to measure angles accurately. For example, you could use a straightedge or a protractor.



This is an example of a straightedge.


This is an example of a protractor.


For this lesson, you will practise using a protractor to measure and draw various angles. A protractor is an instrument for measuring angles, typically in the form of a flat semicircle marked with degrees along the curved edge.

To use a protractor to measure angles, all you do is place the protractor over the angle you want to measure.




Parts of a protractor.


How to measure an angle with a protractor:


  • Place the centre point (or baseline) of the protractor on the vertex of the angle (the point where the sides of the angles meet).
  • Place the 0 mark on one side of the angle (where you see the number 0) — that's actually 0 degrees.
  • Read the measure of the angle where the other side crosses the protractor.


Follow these steps to use a protractor to measure angles.






Note: Be sure you are starting from zero (0).

Click on the Play button below to watch a video on how to use a protractor to measure various angles.




  Self-check!

Try This!

Click here to go to a website where you will practise measuring various angles.

Before you type in your measurement, be sure to ROTATE the protractor so that the horizontal black line of the crossbar lies directly on top of one of the rays.

Images courtesy of www.imagesgoogle.com