See discussion on this mailing list https://groups.google.com/d/topic/redis-db/JaI-paZ0xoA/discussion
Issue #13 : Adds new command: redis-memory-for-key
This command prints the approximate memory used by a key
1. Connect to a running Redis Server
2. Issue dump command and download binary dump of a key
3. Parse the dump using RdbParser
4. Display the memory usage
Added new command redis-memory-for-key, updated readme.