Is there any way to find out how much diskspace a table in MSSQL uses? Or even better, how much diskspace a single row consumes?
For a table you can use
sp_spaceused to determine the size of the table. However, any schema with variable length columns such as varchar/varbinary types will not have a fixed row size. Given that this describes most if not all real databases, you are really only going to be interested in an average row size which can be trivially calculated by dividing the size by the row count.
Somewhat related - this script could be useful: Finding the biggest tables in a database