How to calculate CPTs
This section talks you through the formulae required to calculate the cost of your airtime and how many Television Ratings you can afford to buy.
When it comes to buying airtime, you need have an understanding of what the TV terminology means and also how to use the various formulae to deliver your key calculations.
You can swot up on a wide range of important TV terminology at your leisure in our BARB Glossary, but for the purposes of calculating the cost of TV, you may want to stick on this page and commit these three things to memory:
- TVR: television rating. This is the measure of the popularity of a programme, daypart, commercial break or advertisement by comparing its audience to the population as a whole. One TVR is numerically equivalent to one per cent of a target audience. For example, if Coronation Street achieved a Housepersons TVR of 20 in Yorkshire this means that, on average during the programme, 20% of all Housepersons in the Yorkshire region watched Coronation Street.
- CPT: Cost-Per-Thousand. The cost of one thousand commercial impacts for a target audience. Cost-Per-Thousand (CPT) is used when purchasing and measuring the efficiency of advertising campaigns.
- Universe: the total population of a particular audience category. BARB universes are based on television homes. For example, the network universe for ABC1 Women is the total number of ABC1 Women living within television households in the UK.
The CPTs and TVRs are variable measures, as will be your budget, whereas the universe in a non-variable.
You will always know the universe of the target audience you are buying, as these are published figures. For the most up-to-date universe sizes, take a look on the BARB website.
Equations you will need
There are three key calculations you will need to be able to make when planning your TV campaign. Here’s the questions they set out to answer and the formulae to get to those answers.
How many Television Ratings (TVRs) can I buy?
Ratings = Budget/CPT/universe x 100,000
For example, if you have a budget of £500,000, the CPT is £6.20 and the universe is 48m, you will be able to buy 168 ratings.
£500,000 / £6.20 / 48,000,000 x 100,000 = 168 TVRs
How much will it cost?
Cost = TVRs x CPT x universe / 100,000
For example, if you want to buy 400 TVRs at a CPT of £6.20 with a universe of 48m, it will cost you £1.19m
400 TVRs x £6.20 x 48,000,000 / 100,000 = £1.190, 400
What is the CPT?
CPT = Budget/universe/TVRs x 100,000
For example, if you want to buy 200 TVRs, you have £600,000 to spend and the universe is 48m, the CPT you need to buy is £6.25
£600,000 / 48,000,000 / 200 TVRs x 100,000 = £6.25
How time Lengths affect your calculations
Please note that for all calculation purposes, it is assumed you are buying a 30 second campaign as this is the industry standard. If you are buying different time lengths, you will need to apply a factor.
Time length factors are as follows:
Therefore, looking at how many ratings you can buy with different time lengths, you first need to calculate the 30 second equivalent ratings and then convert them to your specific time length by dividing your 30” equivalent TVRs by your factor.
For example, if you are buying 400 30” equivalent TVRs, this would equate to:
200 60” TVRs (400 30” equiv TVRs / 2.0 = 200 TVRs)
240 50” TVRs (400 30” equiv TVRs / 1.66 = 240 TVRs)
300 40” TVRs (400 30” equiv TVRs / 1.33 = 300 TVRs)
500 20” TVRs (400 30” equiv TVRs / 0.85 = 470 TVRs)
800 10” TVRs (400 30” equiv TVRs / 0.5 = 800 TVRs)
If you are buying a campaign with a variety of different time lengths, you will need to work out an overall time-length factor.