How to use the media GRP calculator
GRP is net reach (%) × average frequency. The mistake made most often is putting a headcount in the reach field. Reach in GRP is the share of the target population contacted at least once, so 40% reach at an average frequency of 3 gives 120 GRP. Enter people instead of a percentage and every number downstream is wrong.
GRP counts 100% as one point and accumulates, so values above 100 are normal. Buying "1,000 GRPs" on a broadcast campaign means enough weight to hit the whole target an average of ten times. When the population is a buying target rather than the general public, the same arithmetic is called TRP (target rating points) — only the population definition changes.
Add total media spend and you get CPP, the cost per GRP point, which is how media and dayparts get compared on price. Add the target population size and you also get people reached, total impressions and CPM, the cost per 1,000 impressions. The table below holds reach steady and varies average frequency from 1 to 5, so you can see how GRP and cost move together. Rate cards differ by contract and season, so enter your own spend rather than trusting a generic number.
Frequently asked questions
Yes. GRP accumulates and includes duplicated contacts, so 50% reach at a frequency of 4 is 200 GRP. A figure above 100 is not a calculation error.
GRP accumulates percentages of a population; impressions count actual contacts. Multiplying by the population size converts one into the other, which is why entering a population here also produces impressions.