Measuring and Drawing Angles
An angle measures the amount of turn between two lines that meet at a point. We measure angles in degrees () using a protractor.
Angles are measured in degrees. A full turn is , a half turn is , and a quarter turn (a right angle) is .
To measure an angle with a protractor:
- Place the centre of the protractor on the vertex (the point where the two lines meet).
- Line up the baseline of the protractor with one arm of the angle.
- Read the scale where the other arm crosses the protractor. Use the scale that starts at on the baseline arm.
To draw an angle:
- Draw a baseline and mark a point for the vertex.
- Place the protractor's centre on the vertex and its baseline along your drawn line.
- Find the required angle on the scale and mark a dot.
- Remove the protractor and draw a line from the vertex through the dot.
Press a button to set the angle. Notice how the arm rotates and the degree reading changes.
Watch it work
Question: Measure the angle shown, then state whether it is acute or obtuse.
Step 1: Place the protractor's centre on the vertex and align the baseline with the lower arm.
Step 2: Read from the on the baseline arm. The other arm crosses the scale at .
Step 3: The angle is . Since , it is acute.
Have a go
Q1. A protractor shows one arm at and the other at . What is the angle?
The angle is .
Q2. Draw an angle of . Which scale on the protractor do you use if your baseline arm is on the left?
Use the inner scale (starting from on the left). Mark a dot at and join it to the vertex.
Q3. Two angles are measured as and . A student says they add up to a full turn. Is the student correct?
. A full turn is .
No. They add up to (a half turn), not a full turn.
Q4. A student measures an angle as but the angle is clearly acute. What mistake have they made?
They have read the wrong scale on the protractor. The correct reading is (using the scale that starts at on the baseline arm).