Protractor
The common protractor is a simple measuring instrument that is typically semicircle in shape with markings from 0° to 180° on it. We use a protractor to measure angles. Architects and designers use a more precise protractor called an angle protractor tool which gives more accurate measures. A compass helps to construct an angle. Set squares, also known as triangle protractor, are used to draw parallel and perpendicular lines. The divider is used to measure the length between two points. Protractors have been in use since the seventeenth century. It is used for navigation in the sea and land. Later by eighteenth century, protractors were widely used in geometry and mathematics.
1.  What is a Protractor? 
2.  How to Use a Protractor? 
3.  Draw and Measure Angles Using Protractor 
4.  Solved Examples on Protractor 
5.  Practice Questions on Protractor 
6.  FAQs on Protractor 
What is a Protractor?
Protractor in maths is considered an important measuring instrument in the geometry box. The protractor tool helps us measure an angle in degrees. A radian scale protractor measures an angle in radians. If you observe closely, a protractor tool has degrees marked from 0 to 180 from left to right in the outer edge and from 180 to 0 in the inner part.
 The inner readings and outer reading supplements each other. i.e, they add up to 180°.
 If the angle to be measured is at the left part of the protractor, we need to use the outer reading of the protractor. ∠AOC = 60°. See in the picture below.
 If the angle to be measured is at the right part of the protractor, we need to use the inner readings of the protractor. ∠BOC = 120°. See in the picture below.
How to Use a Protractor?
An angle is formed between two rays. Let us use the protractor and measure the angle ∠COB. Align the baseline of the protractor with the line AB. The center circle of the protractor at the vertex O. Now, identify the reading on the protractor where ray C is extending.
∠COB = 30°
What do you think is the measure of ∠AOC? Yes, for that we need to look at the outer edge, so ∠AOC=150º. If the angle to be measured is rotated or tilted, tilt your protractor to align with the base ray OA and then measure. Let's see how in the image below.
∠AOB = 45º
Draw and Measure Angles Using Protractor
In this section you are going to learn how to draw and measure angles using a protractor which is very important for us to know to have a complete understanding of protractor. Let us see how to draw an angle of 30º using a protractor.
 Draw a baseline AB.
 Mark the point O and place the center of the protractor at O.
 Align the baseline of the protractor with the line OB.
 In the inner readings, look for 30º and mark it as point C.
 Now using a scale, join O and C.
∠COB = 30°
To measure 220º, a reflex angle, we can write it as 180° + 40°. We can just flip the protractor along the baseline and then mark 40°.
180° + 40° = 220°
Important Notes
 We can also use a 360° protractor to draw this angle. The angle protractor tool and 360° protractor give more precise measurements.
 The symbol for the degree is (°). Always use it while writing the angles. Example (75°, 90°)
 If the angle to be measured is in the left side, use the outer readings of the protractor and if the angle to be measured is in the right side, use the inner readings.
 To reduce errors, align the baseline and vertex properly.
Related Articles on Protractor
Solved Examples on Protractor

Example 1: In triangle ABC, use a protractor and measure ∠CAB.
SolutionPlace the protractor baseline along the line AB and the center of the protractor at vertex A.
Observe the reading in the protractor which overlaps with line AC.∠CAB = 60°

Example 2: What is the angle formed between the two arms of the given pair of scissors?
Solution:
Place the protractor along one arm and measure the angle.
Angle formed = 30° 
Example 3: What is the angle formed at vertex B of the square ABCD?
Solution:Place the protractor center at vertex B of the square and observe the reading.
∠B = 90°
FAQs on Protractor
How to Use a Protractor to Draw Angles?
Protractor is used to measure and to draw angles. Below mentioned are the basic steps to draw angles using protractor.
 Draw a baseline OB.
 Mark the point O and place the center of the protractor at O.
 Align the baseline of the protractor with the line OB.
 Look for the measure to be drawn on the protractor and mark a point C.
 Now using a scale, join O and C.
 COB is a required angle.
How to Use a 360 Degree Protractor?
You can use a 360degree protractor by following these simple steps:
 Place the center of the 360degree protractor at the vertex.
 The 0degree line should be aligned with the baseline of your angle to be measured.
 Observe the number on the 360degree protractor where the other ray is pointing.
How do you Use a Protractor Step by Step?
Protractor is used to measure and to draw angles. Below mentioned are the basic steps to how to use a protractor step by step.
 Align one arm of the angle to be measured with the baseline of the protractor.
 Align the vertex with the center of the protractor.
 Carefully observe the reading on the protractor where the other ray is pointing.
What is a Protractor?
The common protractor is a simple, measuring instrument that is typically semicircle in shape with markings from 0° to 180° on it. We use a protractor to measure and to draw angles.
What is Protractor Used to Measure?
We use a protractor to measure angles that vary from 0° to 360°.
What is the Shape of a Protractor?
Protractor is in the shape of semicircle with markings of angles from 0° to 180 on it. There is one more type of a protractor with which we can measure complete 360 degree angles. It is known as a 360degree protractor and is round in shape.
What is a Triangle Protractor Called?
A triangle protractor is called a set square. A set square (triangular in shape) is a tool used to draw and measure the objects from engineering and technical point of view. Objective of using tool is to provide a straight edge at a right angle or a planar angle to a baseline.