hello,
If you run program "RSTABLESIZE", you can put table name as SOOD on the selection screen. Execute and it will provide the details of the table. The number of lines is actual record count of the table entries and the size is provided under field Memory in KB. Use the division method and find out size in KB for each line. You could also monitor the table and see if the entries are increased you could get the details again and do the division. Compare the old and new size. You could get an approximate value of size of a line from this.
Check these links for the DB02 use -
http://sapbasisdurgaprasad.blogspot.com/2011/06/how-to-check-database-tablespace-sizes.html
best regards,
swanand