STEP 2 Place the origin over the center point, or vertex, of the angle you want to measure. At a glance, we can tell this angle is acute because it is less than 90 degrees. Doing this first step helps you identify which scale to use on the protractor. 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. Obtuse angles are wide (greater than 90 degrees). Īngles can be classified in three ways: acute, obtuse, and right.Īcute angles are narrow (less than 90 degrees). STEP 1 Approximate the measure of your angle. By understanding how the parts of a protractor are used together and following a few easy steps, you will be an angle expert in no time.
How to Use a Protractor to Measure Angles A semi-circular protractor displays a straight angle Generally, semi-circular in shape, protractors are also available in full-circle, 360-degree versions. This makes the tool handy for measuring angles originating from either direction. Most protractors have two opposing ruler grids, one on the inner side of the arc and one on the outer. The measurement scale may seem confusing. Similarly, we could have constructed OM on the 0-degree line first then placed point O on the 30 degree measure to draw OM.At the end of the lesson, the students should be able to use a protractor to measure and draw angles.Ī protractor is a handy tool used to measure and draw angles.
We could also construct ∠OMP by placing OM on the 0 degree line on the right side of the protractor as long as vertex M is centered at the midpoint of the protractor.
Similarly, you can place TV so the vertex is inside the hole of the protractor and lines up with the 0 line to the left side of the protractor. Second, make sure that TV is extended enough such that it goes through the edge of the protractor, then read the degree measure on the inner set of numbers where side TV intersects the protractors edge.First, place side TS so the vertex is inside the hole (the midpoint) of the protractor and TS lines up with the 0 line to the right.Whichever side you line up with the zero-degree line determines which set of numbers to use. When using a protractor, notice that the outside set of numbers goes from 0 to 180 degrees where the 0 is on the left side of the protractor while the inner set goes from 180 to 0 degrees where 0 is on the right side of the protractor. Most protractors measure angles in degrees (°). Home / geometry / angle / protractor ProtractorĪ protractor is a tool used to measure angles.