If you work in radio, advertise on it, or simply follow the industry, you will encounter RAJAR figures regularly. Understanding what those numbers actually measure — and what they do not — is essential to reading them correctly.
RAJAR stands for Radio Joint Audience Research. It is the body responsible for measuring radio audiences in the United Kingdom, established jointly by the BBC and commercial radio industry. Its methodology is based on a continuous weekly survey drawn from a sample of approximately 104,000 respondents across the UK each year.
The primary data collection method is the listening diary. Participants are recruited to keep a record of their radio listening over a seven-day period, noting which stations they listened to and for how long. This diary approach captures habits across all listening contexts — at home, in the car, at work, and via digital devices — and is designed to represent the UK adult population aged fifteen and over.
Two numbers dominate RAJAR reporting. The first is reach, also called weekly reach. This figure tells you how many different people listened to a station for at least five consecutive minutes during the course of a week. A station with a weekly reach of three million has been heard by three million distinct individuals that week. Reach is a measure of audience breadth.
The second key metric is share. Share expresses what percentage of all radio listening hours, across all stations, was spent with a particular station. If all UK adults collectively listened to radio for a hundred hours in a given week, and one million of those hours were spent on a specific station, that station’s share would be one percent. Share is a measure of audience depth and loyalty.
Why do these numbers matter to advertisers? Reach tells you how many people your advertisement could potentially reach. Share tells you how dominant a station is in its listeners’ total radio diet — which in turn speaks to how frequently those listeners are likely to hear a campaign. Combined with demographic breakdowns that RAJAR also provides, advertisers can assess whether a station’s audience matches their target customer profile.
For stations themselves, RAJAR figures determine commercial value and inform scheduling decisions. A morning drive show that significantly outperforms its competitors in reach is worth more to advertisers, and the station can price accordingly. A station losing share quarter on quarter may need to reconsider its format or presentation.
RAJAR publishes its results quarterly, covering rolling periods. Each publication covers the previous twelve months’ data in aggregate, providing a smoothed view that reduces the effect of seasonal variation. Individual quarter-on-quarter shifts are closely watched by the industry.
There are limitations to any diary-based methodology. Recall can be imperfect; listeners may undercount background listening; and online-only listening to international stations falls outside the survey. The industry continues to develop complementary measurement approaches, but RAJAR remains the currency on which UK radio advertising is bought and sold.