Length

Length[expr] gives the number of elements in expr.

Examples

Get the length of a list:

Length[{a, b, c, d, e}]
(* 5 *)

Length of a string (use StringLength for characters):

Length["hello"]
(* 0 - strings have no parts at level 1 *)

StringLength["hello"]
(* 5 *)

Please visit the official Wolfram Language Reference for more details.