How the GRP Calculator works
Gross Rating Points (GRP) are the standard unit media planners use to describe the total weight of an advertising campaign — TV, radio, out-of-home, or digital. GRP combines how many people a campaign reached with how many times, on average, each of them saw it, into a single number that can be compared across flights, markets, and media types.
The formula
GRP is calculated as:
GRP = Reach% x Frequency
where Reach is the percentage of the target audience exposed to the campaign at least once, and Frequency is the average number of times each person in that reached group was exposed. From GRP, total impressions (also called gross impressions) follow as Impressions = GRP x Population / 100. Cost efficiency is then measured with Cost Per Point (CPP) = Media spend / GRP and Cost Per Thousand (CPM) = (Media spend / Impressions) x 1000.
Worked example
Take a target audience of 250,000 people, 45% reach, an average frequency of 4, and a $20,000 media budget. GRP = 45 x 4 = 180. Total impressions = 180 x 250,000 / 100 = 450,000. Cost per point = $20,000 / 180 ≈ $111.11, and cost per thousand impressions = ($20,000 / 450,000) x 1000 ≈ $44.44.
What moves GRP most
- Reach: raising reach without changing frequency increases GRP linearly, but reach itself is capped at 100% of the target audience — you can't reach more people than exist in the group.
- Frequency: raising average frequency also increases GRP linearly and has no upper bound in the formula, which is why heavy campaigns can post GRP totals well over 100.
- Diminishing returns: GRP treats every extra exposure the same, but in practice the tenth time someone sees an ad rarely adds as much value as the second or third — GRP measures campaign weight, not necessarily impact.
GRP vs. TRP vs. reach
Reach alone tells you what share of the audience was exposed at least once, capped at 100%. GRP layers in frequency and can exceed 100 because it counts every exposure, not just unique people. Target Rating Points (TRP) use the identical reach x frequency formula but are calculated only against a specific demographic (for example, adults 25-54) rather than the total population — enter your target demographic's size as the population figure here to get a TRP-equivalent number instead of a general-population GRP.
Where the inputs come from
Reach and frequency estimates typically come from audience measurement services (such as Nielsen for broadcast or comScore-style panels for digital), from a media rep's proposal, or from a platform's own delivery reporting. Because GRP is only as accurate as those inputs, always note the source and measurement period alongside any GRP figure you report.