SELECT table_schema as “Name Of Database”,
sum( data_length + index_length )/1024/1024 as “Size of Data Base in MB”
FROM information_schema.TABLES GROUP BY table_schema ;

This will return size of EACH database on the SQL server. If there are 5 Databases, it will return 5 rows having two columns, first column as name of the DB and second column as its size.