N

N[expr] gives the numerical value of expr.

N[expr, n] attempts to give a result with n-digit precision.

Examples

Numerical approximation:

N[Pi]
(* 3.14159 *)

With specified precision:

N[Pi, 20]
(* 3.1415926535897932385 *)

N[Sqrt[2]]
(* 1.41421 *)

Please visit the official Wolfram Language Reference for more details.