Here are two simple SQL querry that can help you to find it out the size of HANA DB .
we have two aspects here :-
1.column store
2.Row store
to find column store utilization :-
SELECT round (sum(MEMORY_SIZE_IN_TOTAL)/1024/1024) AS "Column Tables MB" FROM M_CS_TABLES;
to find row store utilization :
SELECT round (sum(USED_FIXED_PART_SIZE + USED_VARIABLE_PART_SIZE)/1024/1024) AS "Row Tables MB" FROM M_RS_TABLES;