Billboard’s Top 40 is determined by tabulating music sales, airplay and streaming play. The Billboard Top 40 is actually taken from the Hot 100, a larger list of songs.
While radio and television airplay have become less vital in the face of online streaming and downloading, they still account for a significant portion of a song’s success. Billboard uses Nielsen’s Broadcast Data System to tabulate the frequency with which a song is played on radio and television outlets. The BDS uses pattern-recognition technology to scan the airwaves for a song’s unique signature and keep track of its popularity. The BDS service also estimates the amount of people listening to specific radio stations, providing a more accurate sense of a song’s reach.
Actual music sales are another major factor in determining the Top 40. Billboard uses another Nielsen service, Soundscan, that tracks physical and digital sales of music. Soundscan keeps track of physical releases sold at record stores and digital downloads from iTunes, Amazon.com and other digital marketplaces.
As streaming services become increasingly popular, frequency of plays on YouTube and other sites is now a major determining factor in a song’s chart placement. The precise ratio of sales, airplay and streaming used to determine a song’s popularity varies from week to week, but is typically about 35 to 45 percent sales, 30 to 40 percent airplay and 20 to 30 percent streaming.