What is a Protractor – Definition with Examples

What is a Protractor?

A protractor is a semicircular geometry tool divided into 180 equal parts, each measuring 1°. It is used for drawing angles of known measures and finding angles of unknown measures and is usually made of transparent plastic, glass, steel, or wood. The geometry protractor have two scales marked on it: outer and inner. The outer scale starts from 0° and goes up to 180° in a clockwise direction, and the inner scale has the same range in the counterclockwise direction.

Protractor

How To Measure an Angle Using a Protractor?

Step 1: Place the center point of the protractor over the angle’s vertex.

Vertex of an Angle

Step 2: Adjust the protractor (without shifting the center from the vertex) so that one arm of the angle is along the baseline of the protractor.

Place a Protractor Over an Angle

Step 3: Look at the scale where the baseline arm points to 0 degrees. 

Look for the Baseline Pointing at 0 Degrees

Step 4: Read the measure of the angle where the other arm crosses the scale.

Read the Measure of the Angle

A protractor in math is a very useful tool for measuring angles of different shapes, such as triangles, squares, hexagons, and others. 

How Do You Draw an Angle Using a Protractor?

You can follow the following steps for drawing an angle with a protractor.

Suppose you have to draw an angle of 60°.

  1. Use a ruler to draw a horizontal line AB on the paper.
Draw Line AB using a Protractor
  1. Take a protractor and place it such that its center point coincides with point A and its baseline coincides with AB.
Place a Protractor on the Line AB
  1. Mark point C, where you find a 50° angle on the protractor.
Mark Point C on 50 Degree
  1. Remove the protractor and join points C and A using a ruler.
Join AC to get a 50 Degree Angle
  1. You have drawn an angle of 50° using a protractor.

Solved Examples

Example 1: Find the measure of each angle of an equilateral triangle with the help of a protractor.

Angles of an Equilateral Triangle

Solution: Align the protractor with the vertices of △ABC. Note the angle obtained in each case. You will find that all the angles of the equilateral triangle measure 60°.

Example 2: What will be the angle created at vertex B of the square?

Angle of a Square

Solution: Place the center of the protractor at vertex B with either AB or BC coinciding with the baseline and note the reading. You will get a 90° angle.

Example 3: What is the measure of the angle marked on the following protractor?

Measure Angle Using a Protractor

Solution: The side of the angle lies on the 100° marking of the protractor.

Practice Problems

What is a Protractor - Definition with Examples

Attend this Quiz & Test your knowledge.

1What is the measure of the angle shown in the following right triangle?

What is a Protractor – Definition with Examples
45°
90°
60°
120°
CorrectIncorrect
Correct answer is: 90°
A right angle always measures 90°. You can also use a protractor to confirm the measure.

2What is the measure of the angle shown by the protractor in the following figure?

What is a Protractor – Definition with Examples
70°
65°
75°
67°
CorrectIncorrect
Correct answer is: 67°
Observe the markings on the protractor closely. You will note that the side of the angle lies at 67°.

3What is the measure of the angle shown by the protractor in the following figure?

What is a Protractor – Definition with Examples
180°
176°
170°
175°
CorrectIncorrect
Correct answer is: 175°
Observe the reading on the protractor closely. You will note that the side of the angle aligns with the 175°.

4What is the measure of angle CAB given below?

What is a Protractor – Definition with Examples
100°
105°
75°
120°
CorrectIncorrect
Correct answer is: 75°
Align the protractor on the base AB such that its center coincides with point A. Find the mark with which line AC coincides. Count the markings on the protractor to find ∠CAB = 75°.

Frequently Asked Questions

Protractors are used primarily to design any structure by measuring angles. Engineers use it for creating technical drawings while designing houses, bridges, etc. Carpenters use it for measuring and making furniture.

360° protractor is circular in shape and has readings up to 360°, unlike the usual one with a reading up to 180°.

Two scales are marked on a geometry protractor: one scale goes from 0° to 180° in a clockwise direction and the other scale goes from 0° to 180° in a counterclockwise direction. The scale to use depends on it’s placement.

The center of the protractor is called the origin. It is the point at the bottom of the protractor where the baseline and the perpendicular line intersect.