An angle whose measure is equal to 180°.
A straight angle is an angle that measures exactly 180 degrees. It looks like a straight line because the two rays that form the angle point in exactly opposite directions.
You can think of it like opening a book all the way flat—when the pages lie flat in a straight line, the angle between them is 180°, which makes it a straight angle.
Straight angles help us understand how angles work and how full turns and rotations are measured in geometry.
When Do Students Learn About Straight Angles?
Students are introduced to straight angles when learning about types of angles and measuring angles with degrees.
Grades 4–5 – Introduction to Straight Angles
Students learn to recognize straight angles, measure them, and compare them to other types of angles like acute and obtuse angles.
Grades 6+ – Applying Straight Angles in Geometry
Students use straight angles when working with angle relationships, line segments, and geometric proofs.
