How large are blocks of data in SQL Server?
From the column documentation of sys.database_files:


  size:  Current size of the file, in 8-KB pages.


So a more meaningful query might be something like this:

SELECT
    df.name AS LogicalFileName,
    df.physical_name AS PhysicalPath,
    CONVERT(int, (((df.size * 8192) / 1024.0) / 1024.0)) AS SizeInMB
    FROM sys.database_files df;


(You can expand on that further as necessary.)