How can I get the size in bytes of a table returned by a SQL query in SSMs?
Are you looking for the size of the table, or the size of a row in the table? The latter is only readily available if all your columns are of fixed size, i.e. nchar and not nvarchar etc.
With var sized columns you can use the maximum length of each column, and sum these, to give you a maximum row size, but this really won't accurately reflect your real row sizes.
select sum(max_length)
from sys.columns
where object_id = object_id('MyTable')
You might also create a query that returns DATALENGTH for each column in any particular row to get the total size of only that row.