Measuring Angles
Angles are measured in degrees and a protractor is the tool used to measure and draw angles accurately.
What You Need to Know
Key Concept Diagram
Angles are measured in degrees (°): a full rotation is 360°, a straight line is 180°, a right angle is 90°
Acute angles are less than 90°; obtuse angles are between 90° and 180°; reflex angles are greater than 180°
To use a protractor: place the centre on the vertex, align one arm with 0°, and read where the other arm points
The angles of any triangle always add up to 180°; the angles of any quadrilateral add up to 360°
Key Vocabulary
Angle
The amount of turn between two rays that share a common endpoint (vertex)
Protractor
A semi-circular tool marked in degrees from 0° to 180° used to measure angles
Acute angle
An angle that measures less than 90°
Obtuse angle
An angle that measures more than 90° but less than 180°
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
An angle measures 65°. What type of angle is it?
Question 2
Two angles in a triangle measure 45° and 80°. What is the third angle?
Question 3
Which instrument is used to measure angles?
Key Concepts Summary
- ●Angles are measured in degrees (°): a full rotation is 360°, a straight line is 180°, a right angle is 90°
- ●Acute angles are less than 90°; obtuse angles are between 90° and 180°; reflex angles are greater than 180°
- ●To use a protractor: place the centre on the vertex, align one arm with 0°, and read where the other arm points
- ●The angles of any triangle always add up to 180°; the angles of any quadrilateral add up to 360°