Every track on Spotify has a set of Popularity bars which collectively indicate how popular the track is. Spotify use several algorithms to determine the popularity, but in general the more a song is played the higher its popularity. The popularity rating is based on total number of plays compared to other tracks as well as how recent those plays are.
- Most Popularity views have 12 bars to indicate the popularity. As a song gets more popular, the bars turn white. The more white bars a song has, the more popular it currently is. Songs listed on the Top Lists page have 20 bars though, not 12. And you can resize the Popularity column in the search results, Play Queue, and History list. The wider you make the Popularity column, the more accurately the bars represent popularity.
- The popularity of a track is based on (1) the total number of plays compared to other tracks and (2) how recent those plays are. So over time, if a song isn’t listened to as much as before then its popularity score will go down. If users stop listening to a track, then if it has, say, 6 bars today it may have only 4 bars in a few month’s time.
- New releases on Spotify have all-grey popularity bars to show their fresh, unplayed status. This is often the easiest way to tell what’s new for any given artist: scroll through the list of releases, an album or a single with all-grey playcount bars will most-likely have been added to Spotify only recently.
- Popularity indicators are not updated in real-time. For example, a week after its release, the Muse album The Resistance still has all-grey bars for all its tracks, even though it has undoubtedly been played thousands of times already. Spotify rep Andres was asked a few months ago how often the popularity bars were updated. He said “Not as often as we’d like. We’re working to improve it so it’s updated almost daily.“
- If there are two versions of the same song (for example, one on a single and another on an album), the popularity is separate: if the version on the album has had more plays recently than the version on the single, then it will have a higher popularity score, as if they were two completely different songs. This is also true for duplicates (the same song on two instances of the same album), however when these are grouped in search results the highest popularity is used (not a combination of the two).
- Most albums have a clearly visible popularity curve: the first song is generally more popular than the second, which in turn is usually more popular than the third and so on. This is because casual listeners will move on to something else after a few plays. Greatest Hits albums and compilations are different of course, and you can usually see which songs on an album were singles as their popularity bars spike the trend. Historically artists do not usually sequence their albums with “best song first, worst song last” (indeed, track 7 is often said to always be the best track on an album), but perhaps now that artists have a visualization of listening habits this might affect a new album’s proposed running order.
Sources: Personal observations and Spotify employee responses on getsatisfaction