I would recommend reading the below technote and reviewing the provided script 
as delivered by IBM.  We have modified this to fit our environment, but it is a 
good starting point.

http://www-01.ibm.com/support/docview.wss?uid=swg21596944

Thanks
-Dave

-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT vm.marist DOT edu] On Behalf Of 
Hans Christian Riksheim
Sent: Tuesday, July 28, 2015 9:13 AM
To: ADSM-L AT vm.marist DOT edu
Subject: [ADSM-L] Size of dedup tables in DB2

I would like to calculate the savings of doing dedup. DB2 runs on expensive 
flash, the dedup pool on cheap SATA.

Anyone know how to calculate the extra amount of DB space caused by 
deduplication?

Regards,

Hans Chr.