Naming Conventions

Back to Geometry

The below video covers the written tutorial below - how to name angles based on their size and location.

Naming Angles

Angles can be classified or described based on their size, as well as position relative to a shape. Both of these conventions are covered below.

Naming Angles based on Size

Any angle that is less than 90 degrees is called an acute angle. Right angles are also known as normal angles; and they always measure exactly 90 degrees. An obtuse angle is any angle between 91 degrees and 180 degrees. A reflex angle refers to any angle between 181 degrees and 359 degrees. Knowing this, name the below angles (then roll your mouse over the image to see if you got them right).

Most angles are denoted by a curve, however right angles are usually always marked with a square. This is because all of the angles in a square are 90 degrees.

Naming Angles based on Location

The angles in a shape can be measured either internal to the shape, or external to it. For example, the internal angles of a square are 90 degrees each, however the external angles are 270 degrees each.

It's possible to also have internal and external angles without shapes. Traditionally the smaller of the two angles is called the internal angle, and the larger is called the external angle.