Measure Angles With a Protractor

Measure an angle with a protractor

1. Find the vertex Place the center hole of the protractor exactly on the angle’s vertex. The vertex is the point where the two rays meet.

2. Align one ray with 0° Rotate the protractor so one side of the angle lies along the 0° line. Make sure you are reading the correct scale on the protractor.

3. Read the matching mark Look at where the second ray crosses the protractor scale. Read the number where that ray points. If the protractor has two scales, use the one that starts from 0° on your aligned side.

4. Write the angle measure The measure is given in degrees, such as 35°, 90°, or 125°. If the exercise asks for a final answer, simplify it only if there is any arithmetic to do.

Check your work

• The measure should always be between 0° and 180° for a standard angle drawn with a protractor.
• Recheck that the center is on the vertex and the baseline is lined up with 0°.
• If your answer seems too large or too small, you may have used the wrong scale.

Helpful habit

Measure once carefully, then look again from the aligned 0° side to confirm the reading.