A Gross Rating Point (GRP) is a standard measure used to quantify the reach of an advertising campaign. 1 GRP = 1% reach in the target audience, e.g. 1% viewer ratings. All gross rating points combined give an indication of the distribution between the total reach in the target audience and the average contact frequency.
GRPs are calculated by multiplying the reach percentage with the average contact frequency (reach x number of repetitions).
GRP = reach (%) x average contact frequency
100 GRPs = 100% of the target audience reached once, or 1% of the target audience reached 100 times (or any other possible combination: 20% x 5, 25% x 4, etc.).
How to calculate GRPs:
The used medium has a reach of 60% and the ad is displayed 4x. Number of GRPs = 60% x 4 = 240 GRPs
How to estimate reach and contact frequency in GRPs: You’ve bought 210 GRPs for 175 euro per GRP; total cost is € 36,750. When you allocate your advertising across multiple channels you’ll get a higher reach, with a lower frequency. The distribution would then be, for example, 70% reach x 3 contacts = 210 GRPs. But those same 210 GRPs can also be used with a narrower selection of titles or channels; the total reach would then be lower and the average contact frequency will be higher. The distribution then is, for example, 30% reach x 7 contacts = 210 GRPs.
One of the units (% reach or frequency) is often estimated while the other is calculated.