What Is an Angle?

What Is an Angle?

An angle is created by two rays that have a common end point, called the vertex.

an angle

The angle is also a measure of the rotation between the two rays.

Angles can be measured in degrees (°) or in radians.

How to Identify an Angle

Angles are often identified using Greek letters (α, β, γ, θ, ψ). The letter theta θ is often used.

angle theta

In geometric figures, points are often labelled with capital letters. Consider the angle made between points ABC, where the vertex is A and AB and AC are the rays:


The angle can be identified as the angle A, or by ∠BAC, where the middle of the 3 letters is the vertex.

How to Measure an Angle

An angle is measured by the shortest rotation between the two rays.

Angles are often measure in degrees, denoted °. There are 360 degrees in a full rotation.

Angles can also be measured in radians. There are 2π radians in a full rotation.

Angles can be measured directly using a protractor:

Angles can also be calculated using geometry and trigonometry.

Types of Angles

The different types of angles are:

Type of Angle Description
Acute Less than 90°
Right 90°
Obtuse Greater than 90° but less than 180°
Straight 180°
Reflex Greater than 180°
Full 360°

See Also

What are degrees? What are radians? What is geometry? What is trigonometry?