GRP — what it is and how it is calculated

GRP (Gross Rating Point) is the sum of the ratings of every airing of a spot across a campaign, expressed as a percentage of the target audience. One GRP means one percent of the target audience saw one airing.

How it is calculated

The rating of a single airing is the share of the target audience watching the channel at that moment. A campaign's GRP is the sum of the ratings of all its airings. Which gives the same quantity a second way of being written: GRP = reach × average frequency.

This is why GRP comfortably exceeds 100: forty airings at 5 rating points each make 200 GRP, and that does not mean everyone in the country saw the spot twice — it means the contacts added up to twice the size of the target audience.

What GRP does not tell you

Unique reach. Two hundred GRP can be assembled by showing a spot to ten percent of the audience twenty times, which buys irritation rather than recognition. So GRP is always read alongside reach and frequency, never instead of them.

Why it matters

GRP is the common currency of the TV market: campaign goals are set in it and inventory is sold in it. CPP — the price of one point, and the basis on which channels and slots are compared — is derived from it. In practice what is sold is usually not raw GRP but wGRP, normalised to a base spot length.

In OpenMediaLogic, GRP is calculated as the media plan is built, on your own rate cards and coefficients, and after the campaign the actuals are reconciled against the plan in post-buy.