Grade 4 · Maths · Lessons
Reading the protractor
📐protractor0️⃣zero📏baseline🔢degrees
The protractor.The big ideaStart at zero on the baseline. Read the mark at the second ray.
How it works
Put the centre on the corner and the baseline on one ray.
Start at zero on the baseline. Read the mark where the second ray crosses.
An angle under 90 is acute. 90 is right. More than 90 and less than 180 is obtuse.
Example 1: A right angle
- An angle measures 90 degrees.
- That is exactly a square corner.
- It is a right angle.
Example 2: Read the scale
- The baseline is on the left and the other ray crosses 150.
- Read from the zero on the baseline.
- The angle is 150 degrees. It is obtuse.
Example 3: An acute angle
- An angle measures 45 degrees.
- It is less than 90.
- It is an acute angle.
Words to know
- protractor
- A tool for measuring angles.
- acute
- An angle smaller than a right angle.
- obtuse
- An angle bigger than a right angle.
Watch out
- Start at zero on the baseline.
- A protractor has two scales, so use the one that starts at zero.
- Acute is small, obtuse is wide.
Try it
- Is 30 degrees acute, right or obtuse?
- Is 120 degrees acute, right or obtuse?
- What is a right angle in degrees?
- Where do you put the centre of a protractor?
Answers: 1. acute · 2. obtuse · 3. 90 · 4. on the corner of the angle
For grown-upsMeasure the corners of a book, a door and a clock hand with a protractor.