Use
System Exec function with
cmd/c dir /s "directoryPath" (where
directoryPath is the path to your folder), then parse the size back out of the result.The same approach can be done on Linux or with Powershell.
To parse out folder information from System Exec function's
standard output terminal, use the
Match Pattern Function.
※Note that System Exec function output string will display result in your windows display language, so adjust the Match Pattern function's
regular expressions (1), (2) and (3) to your system display language.

Folder size will display in bytes but you can use
Scale by Power of 2 function to convert the size into your desired unit.

Below is the program settings to parse folder's size and contains out of
System Exec's
standard output terminal (sample program can be downloaded from the attachment files at the bottom of this article).