How to Use a Protractor
Approximate the measure of your angle., Place the origin over the center point, or vertex, of the angle you want to measure., Rotate the protractor to align one leg of the angle with the baseline., Follow the opposite leg of the angle up to the...
Step-by-Step Guide
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Step 1: Approximate the measure of your angle.
Angles can be classified in three ways: acute, obtuse, and right.
Acute angles are narrow (less than 90 degrees), obtuse angles are wide (greater than 90 degrees), and right angles are exactly 90 degrees (two lines perpendicular to each other).You can easily identify by eye, the category of angle you are trying to measure.
Doing this step first helps you identify which scale to use on the protractor.
At a glance, we can tell this angle is acute because it is less than 90 degrees. -
Step 2: Place the origin over the center point
The small hole in the middle of the base of the protractor is the origin.
Align the vertex of the angle with the center of the cross in the origin. , Maintain the vertex of the angle in the origin and gently rotate the protractor so that one of the legs of the angle falls on the baseline of the protractor.
The baseline is parallel to the edge, but is not the flat edge of the protractor.
It is aligned with the center of the origin and the line projects to the start of the scale on either side. , If the line does not pass through the protractor’s arc, extend the angle's line until it does.
Alternatively, you can align the edge of a piece of paper with the angle’s leg to pass beyond the edge of the protractor, continuing the line of the angle.
The number the line passes through is the angle's measurement in degrees.
In the above example, the angle measure is 30 degrees.
We know to use the smaller scale because we determined that our angle was less than 90 degrees in the first step.
If the angle was obtuse, we would use the scale that indicated an angle larger than 90 degrees.
Initially, the measurement scale may seem confusing.
Most protractors have two opposing ruler grids, one on the inner side of the arc and one on the outer.
This makes the tool handy for measuring angles originating from either direction. -
Step 3: or vertex
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Step 4: of the angle you want to measure.
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Step 5: Rotate the protractor to align one leg of the angle with the baseline.
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Step 6: Follow the opposite leg of the angle up to the measurements on the protractor's arc.
Detailed Guide
Angles can be classified in three ways: acute, obtuse, and right.
Acute angles are narrow (less than 90 degrees), obtuse angles are wide (greater than 90 degrees), and right angles are exactly 90 degrees (two lines perpendicular to each other).You can easily identify by eye, the category of angle you are trying to measure.
Doing this step first helps you identify which scale to use on the protractor.
At a glance, we can tell this angle is acute because it is less than 90 degrees.
The small hole in the middle of the base of the protractor is the origin.
Align the vertex of the angle with the center of the cross in the origin. , Maintain the vertex of the angle in the origin and gently rotate the protractor so that one of the legs of the angle falls on the baseline of the protractor.
The baseline is parallel to the edge, but is not the flat edge of the protractor.
It is aligned with the center of the origin and the line projects to the start of the scale on either side. , If the line does not pass through the protractor’s arc, extend the angle's line until it does.
Alternatively, you can align the edge of a piece of paper with the angle’s leg to pass beyond the edge of the protractor, continuing the line of the angle.
The number the line passes through is the angle's measurement in degrees.
In the above example, the angle measure is 30 degrees.
We know to use the smaller scale because we determined that our angle was less than 90 degrees in the first step.
If the angle was obtuse, we would use the scale that indicated an angle larger than 90 degrees.
Initially, the measurement scale may seem confusing.
Most protractors have two opposing ruler grids, one on the inner side of the arc and one on the outer.
This makes the tool handy for measuring angles originating from either direction.
About the Author
Teresa Walker
Experienced content creator specializing in lifestyle guides and tutorials.
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