How to Use Protractors to Measure

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By Tamara Runzel
eHow Contributing Writer

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Protractor

Protractors are common instruments used to measure the degrees of angles. At some point in their schooling, every student will learn how to use a protractor. Protractors commonly are used in geometry to draw angles and also to measure angles and determine the type of angle. Reading a protractor for the first time can seem complicated with all the different numbers. You can learn how to use a protractor with only a few simple tools.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

Protractor Pencil Paper Practice angles

Using a Protractor to Measure

Step 1

Notice the small hole in the center of the bottom of the protractor. This is the vertex point.
Step 2

Place the point of the angle under the vertex point.
Step 3

Line up one arm of the angle on the zero line. The zero line is the line along the bottom of the protractor.
Step 4

Note where that arm passes through zero. If it passes through the numbers on the inside of the protractor, you will use that scale to measure your angle. If it passes through the numbers on the outside, you will use that scale on the protractor to measure your angle.
Step 5

Read the number where the other arm passes through the protractor. That is the measure in degrees of your angle.

Tips & Warnings

Obtuse angles are more than 90 degrees. Acute angles are less than 90 degrees.
Common mistakes when measuring with a protractor include using the wrong scale and not lining up the vertex correctly.