Which Ubuntu Version is equal to which Debian Version

Which Debian Version Ubuntu 14.04 LTS using ?

You can find the Debian version on which your Ubuntu version is based in the file: /etc/debian_version

From 10.04 up to 15.04:

15.04  vivid      jessie / sid
14.10  utopic     jessie / sid
14.04  trusty     jessie / sid
13.10  saucy      wheezy / sid
13.04  raring     wheezy / sid
12.10  quantal    wheezy / sid
12.04  precise    wheezy / sid
11.10  oneiric    wheezy / sid
11.04  natty      squeeze / sid
10.10  maverick   squeeze / sid
10.04  lucid      squeeze / sid

sid is the development distribution of Debian (sid - testing - stable)