Is there a way to convert TRPs (target rating points) to GRPs? I'm comparing two plans and it seems to be apples/oranges. Also, is one metric (TRP or GRP) a better evaluation of the media opportunity than the other?
There are ways to make this conversion. But, the Guru assumes that when you say "GRP" you mean Household rating points. TRPs are simply target GRPs, so if someone mentions GRPs for a given target, that is exactly the same as TRP for that target. If you are getting plans from two sources, you may find that they simply differ in this terminology.
To convert HH to demographic, the process is to examine detailed audience measurements from each vehicle and see how many target impressions are delivered for each household impression. Then divide the target impressions by target universe to calculate TRP. Multiply HH GRP by HH universe to derive HH impressions. Build a ratio between HH GRP and target TRP to create a "conversion factor."
You will find that every daypart, demographic and program has a somewhat different conversion.
However, the Guru believes it is more likely from your question that you are facing the situation of two sources using different terminology.