RMAN SPACE REQUIRMENT FOR RESTORATION ON ASM

Dear Team,

Can you suggest me how much space does the rman require for restoration of database on other server on ASM.

Oracel : 11g Rel 2 (11.2.0.2)

RAC : 2 Node

ASM : Grid Infrastrucure.

I have allocated space depending on the below query output from production[ Database Size]. But while running restore it says space exhusted.

col "Database Size" format a20

col "Free space" format a20

col "Used space" format a20

select  round(sum(used.bytes) / 1024 / 1024 / 1024 ) || ' GB' "Database Size"

,       round(sum(used.bytes) / 1024 / 1024 / 1024 ) -

        round(free.p / 1024 / 1024 / 1024) || ' GB' "Used space"

,       round(free.p / 1024 / 1024 / 1024) || ' GB' "Free space"

from    (select bytes

        from    v$datafile