GRP Calculator (gross rating points = reach × frequency, CPP & CPM)

Understanding the GRP calculator — concept and principle

This calculator works out gross rating points (GRP) for an advertising plan from reach and average frequency, then converts them into gross impressions, people reached, cost per rating point (CPP) and cost per thousand impressions (CPM). Media planners, advertisers and marketing students use it to size TV, radio, outdoor or digital campaigns and to compare plans.

How it is calculated

• GRP = reach (% of target audience) × average frequency
• Gross impressions = GRP ÷ 100 × target audience size
• People reached = reach % × audience size
• CPP = budget ÷ GRP
• CPM = budget ÷ gross impressions × 1,000

The principle

One rating point is an audience equal to 1% of the target population. Adding the ratings of every ad insertion gives gross rating points, which is the same as reach multiplied by average frequency. GRPs measure the total weight of a campaign but say nothing about how it is spread: 200 GRP can mean 100% of people seeing the ad twice or 20% seeing it ten times. That is why reach and frequency are planned together. CPP and CPM put plans of different sizes on a common cost basis. When GRPs are counted for a narrower target group they are often called target rating points (TRP).

Worked example

Defaults: reach 60%, average frequency 3.5, audience 2,000,000 people, budget 150,000.

1. GRP = 60 × 3.5 = 210.
2. Gross impressions = 210 ÷ 100 × 2,000,000 = 4,200,000.
3. People reached = 60% × 2,000,000 = 1,200,000.
4. CPP = 150,000 ÷ 210 = $714.29.
5. CPM = 150,000 ÷ 4,200,000 × 1,000 = $35.71.

How to read the result

More GRPs mean more exposure, but beyond a point extra GRPs mainly raise frequency among people already reached. Compare CPP and CPM across plans and channels, and check that the frequency is high enough for the message to register without wasting money on very heavy exposure. Benchmarks for effective frequency vary by product and medium.

Common mistakes

• Adding reach percentages across channels; reach overlaps, GRPs add.
• Confusing household ratings with ratings for a specific target group.
• Comparing CPM figures based on different audience definitions.
• Assuming GRP alone shows how many people saw the campaign.

Frequently asked questions

What is the difference between GRP and TRP?

GRP is usually based on the whole audience or households; TRP uses a defined target group.

How do I get reach from GRP?

Divide GRP by the average frequency, if you know it. GRP alone cannot tell you reach.

Is a high GRP always better?

No. It increases cost, and much of it may go into repeated exposure of the same people.

Sources: SRDS, "Gross Rating Points (GRP) Calculator" (GRPs and TRPs)