Holds size of the file or directory (lower 32 bits).

A Long value.  

object.Size [= value]

The Size Property syntax has these parts:

This property will contain size of the file or folder (whatever is stored in the item). Typically, it will be presented in bytes, but it is possible that some FTP servers use other form of representation, such as blocks (of whatever size). If size of remote file is larger than 2.7GB, this value can become negative - in which case we suggest you convert it to a double and add MAX_UNSIGNED+1 (4294967296) to it. If size of remote file is larger than 4.2GB, you should also use SizeHi property value.

Just a reminder - you must call ListDir to get directory listing, and then access files through Ftp.DirItems property in order for this property to be available!