Each week, the Radio Songs chart ranks the top 100 songs by most airplay points (frequently referred to as audience impressions, which is a calculation of the number of times a song is played and the audience size of the station playing the tune). A song can pick up an airplay point every time it is selected to be played on specific radio stations that
Billboard monitors. Radio stations across the board are used, from Top 40 Mainstream (which plays a wide variety of music that is generally the most popular songs of the time) to more genre-specific radio stations such as urban radio and country music.
Paid plays of a song or treatment as
bumper music do not count as an impression. During the early years of the chart, only airplay data from top 40 radio stations were compiled to generate the chart. Effective from issue dated July 17, 1993, adult contemporary stations were added to the panel, followed by modern rock few months later. However, beginning in December 1998, the chart profile expanded to include airplay data from radio stations of other formats such as R&B, rock and country. To preserve the notion of the former chart, the
Top 40 Tracks chart (now defunct) was introduced at the same time. Per
Billboard (as of October 2011): "1,214 stations, encompassing pop, adult, rock, country, R&B/hip-hop, Christian, gospel, dance, jazz and Latin formats, are electronically monitored 24 hours a day, 7 days a week by Nielsen Broadcast Data System. This data is used to compile the Billboard Hot 100." The radio airplay data was previously collected on a Wednesday to Tuesday weekly cycle prior to July 2015, and on a Monday to Sunday weekly cycle from July 2015 to July 2021. As of the chart dated July 17, 2021, the radio airplay data is collected on a Friday through Thursday weekly cycle, which matches that of the other Hot 100 metrics (streaming and sales). ==Lists of number ones==