How to Measure Different Types of Angles with a Protractor

Measuring angles with a protractor is easy once you know how to do it. Let’s go through it step-by-step!

1. Get to Know Your Protractor

A protractor usually has two sets of numbers.

• One set measures angles from 0 to 180 degrees.
• A full protractor can measure from 0 to 360 degrees.

Each small mark on the protractor stands for 1 degree. If your angle is bigger than 180 degrees, use the outer numbers.

2. Positioning the Protractor

• Place the Protractor: First, put the center point (the little hole or cross) of the protractor exactly on the angle's vertex. The vertex is where the two lines join.

• Align the Baseline: Make sure one side of your angle is lined up with the straight edge (zero line) of the protractor.

3. Measuring the Angle

• Read the Scale: Check the other side of the angle to see where it touches the numbers. For example, if it touches at the 40-degree mark, then your angle is 40 degrees ($40^\circ$).

• Identify Types of Angles:

  • Acute Angle: Less than 90 degrees (like $45^\circ$).
  • Right Angle: Exactly 90 degrees (makes a perfect corner).
  • Obtuse Angle: Between 90 degrees and 180 degrees (like $120^\circ$).
  • Straight Angle: Exactly 180 degrees (it’s a straight line).

Example

Imagine you need to measure an obtuse angle. After placing the protractor correctly, you see it measures $135^\circ$. Awesome! You’ve found an obtuse angle.

By following these steps, you can measure any angle accurately with your protractor! Happy measuring!