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Measuring an Angle

Measuring an Angle using a Protractor

In every geometry box, there is a protractor, which is commonly used to measure the angles. Some
protractor has degree measure written over it, while some protractor has only the part of lines
visible without any degree markings. Such protractor is called unlabelled protractor.

A protractor is a semicircular tool that is used to draw and measure angles. The markings are
made in two ways: from right to left and vice versa, with markings from 0 to 180°, as you can see
on the labelled protractor shown below.

Unlabelled Protractor Labelled Protractor
How to use a Protractor?

1. Mark a big dot at the vertex of the angle you want to measure and place the centre of your
protractor on the vertex of the angle. The centre of the protractor is the point where the vertical
and horizontal lines intersect.

2. Adjust the protractor in such a way that the base of the angle overlaps the horizontal line
passing through the centre of the protractor.

3. Observe the scale of the protractor and read the marking where the second arm of the angle
coincides. It gives the measure of the angle.

4. The protractor has basically two scales. If the angle you are measuring opens to the left, use
the outer scale (in clockwise direction). If the angle you are measuring opens to the right,
use the inner scale (in anti-clockwise direction). The number of degrees in that angle is the
number that the other line of the angle crosses.

Clockwise Anti-clockwise

The outer The inner
scale scale

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