GRP Calculator

What this calculator does

Media planners need one number to describe the sheer weight of an advertising campaign, so they can compare a television schedule against a radio schedule against a digital buy. The gross rating point is that number, and this calculator produces it in two steps:

Reach percentage = Audience reached ÷ Total audience × 100

GRP = Reach percentage × Frequency

Reach is the share of the audience that saw the advertisement at least once. Frequency is how many times the average person among them saw it. Multiply the two and you have the campaign's gross weight. The calculator returns both figures, and there is a reason it does not just give you the GRP on its own.

Reach times frequency, and why the total can sail past 100

The first thing that confuses people is that GRPs routinely exceed 100. A campaign reaching 30 percent of an audience five times each scores 150 GRPs, and there is nothing wrong with that number.

It happens because GRPs count exposures, not people. Reach counts each person once no matter how many times they saw the ad; that figure genuinely cannot pass 100 percent, because you cannot reach more than everybody. But once you multiply by frequency, you are adding up every viewing, and the same person can be counted many times over. One hundred GRPs simply means the campaign generated exposures equal to one per head of the whole audience. It does not mean everybody saw it once.

Think of it as advertising pressure rather than headcount. GRPs measure how heavily the campaign landed on the market as a whole, in the way that total rainfall measures a storm without telling you which fields got wet. That is a genuinely useful thing to measure, provided you remember what is being counted, because otherwise the number invites exactly the wrong conclusion.

Three figures, and defining the audience first

1. Total audience. The size of the population you are measuring against.
2. Audience reached. How many distinct people saw the advertisement at least once. Distinct is the operative word: this is people, not views.
3. Frequency per viewer. The average number of times each reached person saw it.

The first input carries more weight than it looks. If total audience means the entire population of a market, you are computing conventional gross rating points. If it means a specific target group, say women aged 25 to 44, you are computing what the industry calls target rating points, or TRPs, which is the same arithmetic applied to a narrower base.

The distinction changes the answer dramatically. An advertisement reaching everybody in a market once scores 100 GRPs, but if only 35 percent of that market is in your target group, the same schedule delivers only 35 TRPs against the people you actually care about. Neither figure is wrong; they answer different questions. Decide which you are asking before entering the total audience, and label the result accordingly.

The same 200 GRPs, four different campaigns

Here is the demonstration that matters most, and the reason this calculator shows reach separately rather than burying it. Every one of the following media plans delivers exactly 200 GRPs.

• Reach 100 percent, frequency 2: 200 GRPs. Everybody sees it twice.
• Reach 50 percent, frequency 4: 200 GRPs. Half the market sees it four times, half never sees it.
• Reach 25 percent, frequency 8: 200 GRPs. A quarter of the market is saturated; three quarters have no idea the campaign exists.
• Reach 20 percent, frequency 10: 200 GRPs. One person in five sees the advertisement ten times.

Identical weight, four completely different campaigns, and they would suit completely different objectives. Launching a new product that nobody has heard of? The first plan is obviously right, because the second and third leave most of the market unaware the product exists. Trying to shift a stubborn habit among a known group, where research says people need several exposures before anything sinks in? Then the concentration of the third or fourth plan is doing the work, and spreading the same budget thinly would waste it.

This is why experienced planners never judge a schedule on GRPs alone. The GRP tells you how much pressure you bought. Reach and frequency tell you how that pressure was distributed, and the distribution is where the campaign either works or does not.

What the number deliberately does not tell you

Worth being clear about the boundaries, because GRPs get quoted as though they measured success and they do not measure anything of the sort.

They say nothing about quality. Two hundred GRPs of a brilliant advertisement and 200 GRPs of a forgettable one are the same number. The metric counts opportunities to see, not attention paid, not memory formed, and certainly not anything bought.

They say nothing about cost. A schedule delivering 200 GRPs cheaply and one delivering 200 GRPs expensively look identical here. That is what the related cost per point measure is for, dividing total media spend by GRPs to get the price of each point, which is how planners actually compare the efficiency of competing plans.

And frequency is an average, which hides its own distribution. An average of four exposures might mean almost everyone saw it four times, or that most saw it once while a small group saw it fifteen times. Planners deal with this by looking at effective frequency, the share of the audience reached at least some minimum number of times, often three, on the reasoning that one or two exposures rarely register.

None of that makes GRPs a poor measure. It makes them a measure of one specific thing, campaign weight, which they capture well and which is genuinely hard to express any other way across different media. Use them to compare the heft of alternative plans, then use reach, frequency and cost per point to work out whether that heft is landing where you need it.

Questions people ask

Does 100 GRPs mean everyone saw my ad?

No. It means total exposures equalled one per person in the audience. That could be everybody once, half the audience twice, or a quarter four times. Check the reach figure to find out which.

Can GRPs go above 100?

Yes, routinely. Reach cannot exceed 100 percent, but multiplying by frequency counts repeat exposures, so campaign totals of several hundred GRPs are normal.

What is the difference between GRP and TRP?

The same calculation on a different base. GRPs measure against the whole population, TRPs against a specific target demographic. A schedule delivering 100 GRPs may deliver far fewer TRPs.

How many GRPs should a campaign buy?

There is no universal figure, since it depends on the objective, the medium and the competition. The more useful question is whether the reach and frequency split suits what you are trying to achieve, and what each point is costing you.

References

Gross rating points are the product of reach, the percentage of homes or persons exposed at least once to a schedule, and frequency, the average number of exposures among those reached. Because reach excludes duplication while GRPs do not, the same GRP total can be produced by very different combinations of reach and frequency, and the sum of ratings against a specific demographic segment is conventionally described as target rating points.

1. SRDS, Gross Rating Points and Target Rating Points. https://srds.com/calculator/grps-trps/
2. Digiday, What is a GRP, or gross rating point? https://digiday.com/marketing/what-is-a-grp-gross-ratings-point/