Straight angleAlso Flat Angle
Definition: An angle whose measure is exactly 180° - a straight line
Try this Adjust the angle below by dragging an orange dot and see how the angle ABC behaves. Note that it is a Straight Angle only when it is exactly 180°

Straight (or Flat) angles are formed when the legs are pointing in exactly opposite directions. The two legs then form a single straight line through the vertex of the angle. The measure of a flat angle is thus always 180°

Types of angle

Altogether, there are six types of angle as listed below. Click on an image for a full description of that type and a corresponding interactive applet.

Acute angle Right Angle Obtuse Angle
Acute angle
Less than 90°
Right angle
Exactly 90°
Obtuse angle
Between 90° and 180°
Straight Angle Reflex Angle Full Angle
Straight angle
Exactly 180°
Reflex angle
Between 180° and 360°
Full angle
Exactly 360°

Related angle topics


Angle Types

Angle relationships