Gross rating point
In advertising, a Gross rating point (GRP) is a measure of the size of an advertising campaign or by a specific medium or schedule. It does not measure the size of the audience reached. Rather, GRPs quantify impressions as a percentage of the target population, and this percentage may thus be greater than, or in fact much greater than, 100. Target rating points express the same concept, but with regard to a more narrowly defined target audience.
GRPs are used predominantly as a measure of media with high potential exposures or impressions.
The purpose of the GRP metric is to measure impressions in relation to the number of people in the target for an advertising campaign. GRP values are commonly used by media buyers to compare the advertising strength of components of a media plan.
GRPs are most directly calculated by summing the ratings of individual ads in a campaign. If a television program has an average rating of 7, and an ad is placed on 5 episodes, then the campaign has 35 = 7 × 5 GRPs.
GRPs are simply total impressions related to the size of the target population:
- GRPs (%) = 100 * Impressions (#) ÷ Defined population (#) 
GRPs can also be related to measures of the reception of the ad campaign. If an ad campaign results in 50% of the target seeing the advertising 3 times on average, then the campaign's size was 150 GRPs:
- GRPs (%) = Reach (%) × Average frequency (#)
- Farris, Paul W.; Neil T. Bendle; Phillip E. Pfeifer; David J. Reibstein (2010). Marketing Metrics: The Definitive Guide to Measuring Marketing Performance. Upper Saddle River, New Jersey: Pearson Education, Inc. ISBN 0-13-705829-2. The Marketing Accountability Standards Board (MASB) endorses the definitions, purposes, and constructs of classes of measures that appear in Marketing Metrics as part of its ongoing Common Language in Marketing Project.
- American Marketing Association Dictionary. http://www.marketingpower.com/_layouts/Dictionary.aspx. Retrieved 2013-2-11. The Marketing Accountability Standards Board (MASB) endorses this definition as part of its ongoing Common Language in Marketing Project.