Year 5: Measuring and drawing angles with a protractor
Part of the Year 5 angles and shapes chapter. Chapter overview · whole chapter on one page
Measuring and drawing angles with a protractor
A protractor measures angles in degrees. Put the centre of the protractor on the corner of the angle, which is the vertex. Line up one arm with the 0 line. Then read the number where the other arm crosses the scale.
To draw an angle, make a dot at the number on the scale, then join the dot to the vertex. Always estimate first, so you can check that your answer makes sense.
Key ideas
- Put the centre of the protractor on the vertex.
- Line up one arm with the 0 line.
- Read the scale where the other arm crosses it.
- A protractor measures up to 180°. A reflex angle must be worked out another way.
Key words. A protractor measures angles. Its centre goes on the vertex, and one arm lies along the 0 line.
Method. Put the centre on the vertex, line up the 0 line and read the scale where the other arm crosses it.
- Put the centre of the protractor on the vertex. The centre must be at the corner of the angle.centre on the vertex
- Line up one arm with the 0 line. Then the scale starts at 0 on that arm.start at 0 on the base line
- Read the number where the other arm crosses the scale. Count the scale in 5s and 10s to find the number.the arm crosses the scale at 65
- Write the answer with the degree sign. The angle is acute.65°
Check. 65° is acute, which matches the picture. ✓
Watch out. Read the scale that starts at 0 on the arm you lined up. Do not read the other scale by mistake.
Key words. A protractor measures angles. Its centre goes on the vertex, and one arm lies along the 0 line.
Method. Draw one arm, put the protractor on it, mark the angle, then draw the second arm.
- Draw one straight arm. This arm is the 0 line.one arm drawn
- Put the centre on the end of the arm. The end of the arm is the vertex, where the two arms meet.centre on the vertex
- Find the number on the scale and make a dot. Count round the scale to the number in the question.dot at 110°
- Join the dot to the vertex. The second arm makes the angle.110° angle drawn
Check. Measure your drawing: it should read 110°. ✓
Watch out. Use the scale that starts at 0 on the arm you drew.
Key words. Angles on a straight line add up to 180°, which is a half turn. Angles at a point add up to 360°, which is a whole turn.
Method. Find the whole turn, then take away the small angle.
- Write the size of a full turn. A full turn is 360°.360°
- Take away the small angle. The rest of the turn is the reflex angle.360 − 130 = 230
- Write the answer. 230°
Check. 130 + 230 = 360, so the two angles make a full turn. ✓
Watch out. A protractor cannot measure a reflex angle directly. Work it out from the small angle.
Watch out
A common mistake is to read the wrong scale. A protractor has two scales. Use the one that starts at 0 on the arm you lined up. Also, a protractor only measures up to 180°.
Exercise 9C Measuring and drawing angles
Non-calculatorKey words. A protractor measures angles. Its centre goes on the vertex, and one arm lies along the 0 line.
Method. Put the centre on the vertex, line up the 0 line and read the scale where the other arm crosses it.
- Put the centre of the protractor on the vertex. The centre must be at the corner of the angle.centre on the vertex
- Line up one arm with the 0 line. Then the scale starts at 0 on that arm.start at 0 on the base line
- Read the number where the other arm crosses the scale. Count the scale in 5s and 10s to find the number.the arm crosses the scale at 40
- Write the answer with the degree sign. The angle is acute.40°
Check. 40° is acute, which matches the picture. ✓
Watch out. Read the scale that starts at 0 on the arm you lined up. Do not read the other scale by mistake.
Key words. A protractor measures angles. Its centre goes on the vertex, and one arm lies along the 0 line.
Method. Put the centre on the vertex, line up the 0 line and read the scale where the other arm crosses it.
- Put the centre of the protractor on the vertex. The centre must be at the corner of the angle.centre on the vertex
- Line up one arm with the 0 line. Then the scale starts at 0 on that arm.start at 0 on the base line
- Read the number where the other arm crosses the scale. Count the scale in 5s and 10s to find the number.the arm crosses the scale at 115
- Write the answer with the degree sign. The angle is obtuse.115°
Check. 115° is obtuse, which matches the picture. ✓
Watch out. Read the scale that starts at 0 on the arm you lined up. Do not read the other scale by mistake.
Key words. A protractor measures angles. Its centre goes on the vertex, and one arm lies along the 0 line.
Method. Put the centre on the vertex, line up the 0 line and read the scale where the other arm crosses it.
- Put the centre of the protractor on the vertex. The centre must be at the corner of the angle.centre on the vertex
- Line up one arm with the 0 line. Then the scale starts at 0 on that arm.start at 0 on the base line
- Read the number where the other arm crosses the scale. Count the scale in 5s and 10s to find the number.the arm crosses the scale at 150
- Write the answer with the degree sign. The angle is obtuse.150°
Check. 150° is obtuse, which matches the picture. ✓
Watch out. Read the scale that starts at 0 on the arm you lined up. Do not read the other scale by mistake.
Key words. A protractor measures angles. Its centre goes on the vertex, and one arm lies along the 0 line.
Method. Put the centre on the vertex, line up the 0 line and read the scale where the other arm crosses it.
- Put the centre of the protractor on the vertex. The centre must be at the corner of the angle.centre on the vertex
- Line up one arm with the 0 line. Then the scale starts at 0 on that arm.start at 0 on the base line
- Read the number where the other arm crosses the scale. Count the scale in 5s and 10s to find the number.the arm crosses the scale at 25
- Write the answer with the degree sign. The angle is acute.25°
Check. 25° is acute, which matches the picture. ✓
Watch out. Read the scale that starts at 0 on the arm you lined up. Do not read the other scale by mistake.
Key words. A protractor measures angles. Its centre goes on the vertex, and one arm lies along the 0 line.
Method. Put the centre on the vertex, line up the 0 line and read the scale where the other arm crosses it.
- Put the centre of the protractor on the vertex. The centre must be at the corner of the angle.centre on the vertex
- Line up one arm with the 0 line. Then the scale starts at 0 on that arm.start at 0 on the base line
- Read the number where the other arm crosses the scale. Count the scale in 5s and 10s to find the number.the arm crosses the scale at 75
- Write the answer with the degree sign. The angle is acute.75°
Check. 75° is acute, which matches the picture. ✓
Watch out. Read the scale that starts at 0 on the arm you lined up. Do not read the other scale by mistake.
Key words. A protractor measures angles. Its centre goes on the vertex, and one arm lies along the 0 line.
Method. Put the centre on the vertex, line up the 0 line and read the scale where the other arm crosses it.
- Put the centre of the protractor on the vertex. The centre must be at the corner of the angle.centre on the vertex
- Line up one arm with the 0 line. Then the scale starts at 0 on that arm.start at 0 on the base line
- Read the number where the other arm crosses the scale. Count the scale in 5s and 10s to find the number.the arm crosses the scale at 135
- Write the answer with the degree sign. The angle is obtuse.135°
Check. 135° is obtuse, which matches the picture. ✓
Watch out. Read the scale that starts at 0 on the arm you lined up. Do not read the other scale by mistake.
Key words. Angles on a straight line add up to 180°, which is a half turn. Angles at a point add up to 360°, which is a whole turn.
Method. Add the known angles at a point, then take them away from 360.
- Add the parts we know. The angles at a point that we know are 130.130
- Take this away from 360. The angles at a point add up to 360, so the missing one is what is left.360 − 130 = 230
- Write the answer. 230°
Check. 130 + 230 = 360. ✓
Watch out. Do not add the missing part to the total. Take the known parts away from the total.
Key words. A protractor measures angles. Its centre goes on the vertex, and one arm lies along the 0 line.
Method. Check each part of the drawing: the centre, the 0 line and the scale.
- Check where the centre was. The centre must be on the vertex, the corner of the angle.centre not on the vertex
- Check the 0 line. One arm must lie along the 0 line of the scale.the 0 line was not lined up
- Measure again. Read the scale that starts at 0 on the arm.55° is the correct size
Check. Measure the drawing again: it should read 55°. ✓
Watch out. A small mistake in the centre or the 0 line gives the wrong answer.
Key words. A protractor measures angles. Its centre goes on the vertex, and one arm lies along the 0 line.
Method. Draw one arm, put the protractor on it, mark the angle, then draw the second arm.
- Draw one straight arm. This arm is the 0 line.one arm drawn
- Put the centre on the end of the arm. The end of the arm is the vertex, where the two arms meet.centre on the vertex
- Find the number on the scale and make a dot. Count round the scale to the number in the question.dot at 70°
- Join the dot to the vertex. The second arm makes the angle.70° angle drawn
Check. Measure your drawing: it should read 70°. ✓
Watch out. Use the scale that starts at 0 on the arm you drew.
Key words. A protractor measures angles. Its centre goes on the vertex, and one arm lies along the 0 line.
Method. Draw one arm, put the protractor on it, mark the angle, then draw the second arm.
- Draw one straight arm. This arm is the 0 line.one arm drawn
- Put the centre on the end of the arm. The end of the arm is the vertex, where the two arms meet.centre on the vertex
- Find the number on the scale and make a dot. Count round the scale to the number in the question.dot at 125°
- Join the dot to the vertex. The second arm makes the angle.125° angle drawn
Check. Measure your drawing: it should read 125°. ✓
Watch out. Use the scale that starts at 0 on the arm you drew.
Key words. A protractor measures angles. Its centre goes on the vertex, and one arm lies along the 0 line.
Method. Put the centre on the vertex, line up the 0 line and read the scale where the other arm crosses it.
- Put the centre of the protractor on the vertex. The centre must be at the corner of the angle.centre on the vertex
- Line up one arm with the 0 line. Then the scale starts at 0 on that arm.start at 0 on the base line
- Read the number where the other arm crosses the scale. Count the scale in 5s and 10s to find the number.the arm crosses the scale at 170
- Write the answer with the degree sign. The angle is obtuse.170°
Check. 170° is obtuse, which matches the picture. ✓
Watch out. Read the scale that starts at 0 on the arm you lined up. Do not read the other scale by mistake.
Key words. A protractor measures angles. Its centre goes on the vertex, and one arm lies along the 0 line.
Method. Estimate first, then measure.
- Estimate first. The arm is past the right angle line, so the angle is more than 90°.more than 90°
- Measure with the protractor. Put the centre on the vertex and line up the 0 line, then read the scale.the arm crosses the scale at 110
- Write the answer. The estimate and the measurement agree.110°
Check. 110° is more than 90°, which matches the estimate. ✓
Watch out. An estimate tells you which scale and which end of the scale to read.