What measures are used to gauge radio listening?

Although children and teenagers do fill in the RAJAR diaries that record their radio listening, most stations use the 15+ population as their audience base. Listening by under 15s is then used separately, as required.

One of the main audience measurements for radio is Weekly Reach. This is the number of people (or percentage of a population) that heard a station for at least five minutes in a given week. So if every single member of BBC Radio Kent's area population that is over 15 years old heard BBC Radio Kent in a week, its reach would be 100%.

Share of listening is a measure of how much of all listening to the radio is directed to a certain station. So if half of all radio listening in the UK was people listening to Radio 2, then its share of all listening would be 50%. Share to a station is boosted by having a core listenership that listens heavily through the week, while listeners that tune in and out for a specific purpose (like sport or traffic news) are more likely to boost reach.

Another measure sometimes used is hours per listener. This shows how long an average listener listens to a station for in a week. The higher the average, the higher share of listening is likely to be. However, this is not always the case - a station might have a high weekly reach, which means that many of its listeners don't listen for sustained periods and therefore bring the hours per listener average down. Alternatively, a station might have a very loyal core audience which pushes the average up, but which is too small to make a big impression on the share of all listening to radio.