web interface port for oracle 11g
The default port used for dbcontrol is 1158. You may have changed the port though, of course.

The emctl control commands also display the 'about' URL which includes the port number. For example:

$ emctl status dbconsole
Oracle Enterprise Manager 11g Database Control Release 11.2.0.3.0
Copyright (c) 1996, 2011 Oracle Corporation.  All rights reserved.
https://myhost.mydomain.com:1158/em/console/aboutApplication
...