The four types of angle you should know are acute, obtuse, reflex and right angles. When you are estimating the size of an angle, you should consider what type of angle it is first.
An acute angle is less than .
A right angle is exactly .
An obtuse angle is between and .
A straight angle or an angle on a straight line is exactly .
A reflex angle is between and .
A full turn or complete revolution is exactly .