The primary measurement metric for all online media including Internet radio is the impression. Impressions are a simple, basic measurement unit. One person exposed one time to one ad equals one impression. But using impression based measurement does not mean that GRP metrics are obsolete. GRPs have long been the standard for traditional media planners and buyers. Converting Internet radio or interactive campaigns to Gross Rating Points can be useful because enables a planner to make cross media comparisons.
You won’t find Gross Rating Points reported on interactive research tools, but it’s a simple math formula that can easily be integrated into a spreadsheet. A GRP (Gross Rating Point) is 1% of the measured audience. For Internet radio purposes and for the sake of consistency, I recommend using the Arbitron definition of the measured audience, either for a certain market or entire US, but this is certainly a point to discuss with the planner or media buyer. Once you define the market the formula is
# of impressions / defined market population = GRPs
There’s no reason you can’t use the same formula to compute banner, mobile, video or other impression values. This is an easy way for radio and Internet radio sellers to begin to quantify the value of packages that include audio impressions, banner impressions, and perhaps other assets as well. Impressions do not tell the whole story, but this is one way to educate buyers on the value that they are getting from the cross media package you are selling.