How to determine the size of my tables in the SQL Server database
If you don't want to write a script, you can also open the much underused 'Object Explorer Details' in SSMS (Shortcut key F7).



From the Top-Level, open the Tables folder to get a list of all the tables in your database.

You may need to customise the columns to see the Space Used. This can be done by right clicking on the header row and choosing the columns you wish to display.



There's plenty more data like this available in Object Explorer Details.