What are the types of angles?
Year 3 recognises right angles, Year 4 acute and obtuse angles, Year 5 measures in degrees and meets reflex angles, and Year 6 finds missing angles. Below: what it means, a worked example, the mistake to watch for and an 11+ question.
The answer
Angles are named by their size: acute is less than 90°, right is exactly 90°, obtuse is between 90° and 180°, and reflex is between 180° and 360°.
What it means
An angle is the amount of turn between two lines that meet. It is measured in degrees (°).
A straight angle is exactly 180°, and a full turn is 360°.
Angles on a straight line add up to 180°, and angles round a point add up to 360°.
A worked example
Name each angle: 35°, 90°, 135°, 200°
- 35° is less than 90°: acute.
- 90° exactly: a right angle.
- 135° is between 90° and 180°: obtuse.
- 200° is more than 180°: reflex.
The common mistake
Reading the wrong scale on a protractor and writing 140° for an angle of 40°. Decide first whether the angle is acute or obtuse, then check the reading agrees.
How it comes up in the 11+
Two angles sit together on a straight line. One is 118°. What is the other, and what type of angle is it?
Answer: 62°, an acute angle
- Angles on a straight line add up to 180°.
- 180 − 118 = 62, so the other angle is 62°.
- 62° is less than 90°, so it is acute.
Related words and practice
More maths words
Questions parents ask
Is 90° acute or obtuse?
Neither. An angle of exactly 90° is a right angle. Acute is less than 90° and obtuse is more.
What is a reflex angle?
An angle bigger than 180° but less than 360°. It is the angle on the outside when two lines meet.
Knowing the words is half of an 11+ maths question
11+ papers use maths vocabulary without explaining it. The free diagnostic checks maths, English and both kinds of reasoning, and shows what to practise next. No card is required.