VectorAngle

VectorAngle[u, v] gives the angle between the vectors u and v.

Examples

Angle between 2D vectors:

VectorAngle[{1, 0}, {0, 1}]
(* Pi/2 *)

Angle between 3D vectors:

VectorAngle[{1, 0, 0}, {1, 1, 0}]
(* Pi/4 *)

Please visit the official Wolfram Language Reference for more details.