Measuring angles

Measuring Angles Using a Protractor

The size of an angle is measured in degrees (˚). Think of a circle which is divided into 360 equal sectors. Each sector has a small angle at the centre 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 angle ABC ,

How do we measure the size of the angle?

We can measure angles using an instrument known as a protractor.

A protractor

The 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.

To measure angle ABC , we need to:

Step 1: Place the centre 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.

If the angle is facing the other way, we could use the outer scale to measure it.

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

Measure angles using a protractor (part 1)

Draw and measure angles using a protractor (part 2)

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