Measuring Angles With A Protractor
Concept
The size of an angle depends on how wide or narrow the opening between its two sides is. This opening is measured in degrees. There are 360 degrees in a full rotation.
A protractor is a tool that measures the number of degrees in an angle.
Rules
To measure an angle using a protractor, follow the steps below.
1. Line up the vertex of the angle with the dot at the center of the protractor.
2. Line up one side of the angle with 0 degrees on the protractor.
3. Read the protractor to see where the other side of the angle crosses the number scale.
Example
What is the degree measure of the given angle?
Solution
1. On the given protractor, one line is lined up with zero on the outer scale.
2. Read along the outer scale, starting from the zero where the first line is placed. Where the other line crosses, the scale is the angle.
Answer: 110°
Practice How to Use a Protractor
Practice Problem 1
What is the degree measure of the given angle?
Practice Problem 2
What is the degree measure of the given angle?
Practice Problem 3
What is the degree measure of the given angle?
An angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle.
Vertex of the angle – The sides of an angle are two rays that share a common endpoint. The vertex of an angle is the point where the two sides of an angle meet.
A protractor is used to measure and draw angles. There are two sets of degrees along the edge of the protractor: an inner and outer scale. Both scales go from 0 to 180 degrees, but they run in opposite directions. Each mark on the protractor is 1 degree.
The baseline, also known as the zero edge, has a small circle at its midpoint. This is the center mark or origin point.
Pre-requisite Skill
Classify Angles