List of Nielsen ratings (TRS)
From Battlestar Wiki, the free, open content Battlestar Galactica encyclopedia and episode guide
Note that the methodology for the ratings changed during the timespan in which the series was originally broadcast. The ratings available before 2008 (Seasons 1-3 and Razor) do not factor delayed viewing (DVRs, etc.), whereas the ones for 2008 (Season 4.0) take the same day viewers into account in addition to the live viewers. In addition, with Sci Fi Wire no longer publishing the free 'Nielsen Galaxy Report', the only numbers available for 2009 (Season 4.5) are in fact the total number of viewers. To provide comparable numbers, the ratio between the number of total viewers and the household rating was used to scale the ratings for the rest of Season 4.5 episodes.