ByteCount

ByteCount[expr] gives the number of bytes used internally by the Wolfram System to store expr.

Examples

Check memory usage of expressions:

ByteCount[{1, 2, 3, 4, 5}]
(* 136 *)

Compare memory for different types:

ByteCount[Range[1000]]
(* 8056 *)

ByteCount["Hello World"]
(* 104 *)

Please visit the official Wolfram Language Reference for more details.