What are the main types of angle?
An acute angle is less than 90°, a right angle is exactly 90°, an obtuse angle is between 90° and 180°, a straight angle is exactly 180°, and a reflex angle is more than 180° but less than 360°.
// maths › Angles
Angles & angle types
Classify any angle as acute, right, obtuse, straight, or reflex, and find its complement and supplement, with a live protractor dial that sweeps to the angle you enter and names its type instantly.
acute < 90° · right = 90° · obtuse 90–180° · straight = 180° · reflex 180–360°
Frequently asked questions
What is the difference between complementary and supplementary angles?
Complementary angles add up to 90°, while supplementary angles add up to 180°. For example, 30° and 60° are complementary, and 110° and 70° are supplementary.
Can you give a worked example?
Take 135°. It is larger than 90° but smaller than 180°, so it is obtuse. It has no complement (only angles under 90° do), but its supplement is 180° − 135° = 45°.
Why does a reflex angle go beyond 180°?
A reflex angle measures the larger opening between two rays — the way round that is more than a straight line. Every angle below 180° has a reflex partner that completes the full 360° turn.
Where is this used in real life?
Carpenters and builders check right angles for square corners, navigators and pilots work with reflex and acute bearings, surveyors measure angles of slopes, and graphic designers and animators rotate objects by precise angles.