When you view a file in Windows Explorer you see only the file
data and the size of the file data - never the size of the metadata
associated with that file.
The Length property holds the number of bytes of data for all
metadata associated with the file. If you add this to the size of
the file you will get the total number of bytes of disk space used
by the file.
The Field Length is the same value as you would obtain by
iterating through every metadata stream in the file and summing the
lengths of each of these items of metadata.