There isn´t any easy way to do this(what I know of..).
You could do it the hard way though!
If you have your db-design ready you could calulate how much space a row in a table will allocate..
If you have table that consists of two fields: ID(Integer), SName(Varchar(100), you know that each row in the table will alocate maximum 104bytes(Inteder=4 and Varchar=max100).
SQLServer stores information in pages(think the size is 8k), now you can calculate how many rows each page can contain(There is more information by default in the page so count with 7,9k).
Now you also know how many pages there is in 1Mb (1024/8 = 128). So let´s say that your calculation shows that you can have 76rows in each page for the table above and there is 128 pages in 1Mb you now know that 9728 rows = 1Mb(for that table)..
I´ts up to you if you wan´t to spend the time it takes to do this calculation...