The album-equivalent unit was introduced in the mid-2010s as an answer to the drop of album sales in the 21st century.
Album sales more than halved from 1999 to 2009, declining from a $14.6 to $6.3 billion industry.
The usage of the album-equivalent units revolutionized the charts from the "best-selling albums" ranking into the "most popular albums" ranking.
The International Federation of the Phonographic Industry (IFPI) have used album-equivalent unit to measure their Global Recording Artist of the Year since 2013.
Uses on record charts and certifications
Beginning with the December 13, 2014, issue, the Billboard 200 albums chart revised its ranking methodology with album-equivalent unit instead of pure album sales.
With this overhaul, the Billboard 200 includes on-demand streaming and digital track sales (as measured by Nielsen SoundScan) by way of a new algorithm, utilizing data from all of the major on-demand audio subscription services including Spotify, Apple Music, Google Play, YouTube and formerly Xbox Music.
Known as TEA (track equivalent album) and SEA (streaming equivalent album) when originally implemented, 10 song sales or 1,500 song streams from an album were treated as equivalent to one purchase of the album.
Billboard continues to publish a pure album sales chart, called Top Album Sales, that maintains the traditional Billboard 200 methodology, based exclusively on Nielsen SoundScan's sales data.
Taylor Swift's 1989 was the first album to top the chart with this methodology, generating 339,000 album-equivalent units (281,000 units came from pure album sales).
In Billboard's February 8, 2015, issue, Now That's What I Call Music! became the first album in history to miss the top position of the Billboard 200 despite being the best-selling album of the week. 53
In July 2018, Billboard and Nielsen revised the ratios used for streaming equivalent album units to account for the relative value of streams on paid music services like Apple Music or Amazon Music Unlimited versus ad-supported music and video platforms such as Spotify's free tier and YouTube.
Under the updated album equivalent ratios, 1,250 premium audio streams, 3,750 ad-supported streams, or 3,750 video streams are equal to one album unit.
Similarly the Recording Industry Association of America, which had previously certified albums based on units sold to retail stores, began factoring streaming for their certifications in February 2016.
The change was decided after the massive growth of streaming; the number of tracks streamed in the UK in a year doubled from 7.5 billion in 2013 to just under 15 billion in 2014.
Under the new methodology, Official Charts Company takes the 12 most-streamed tracks from an album, with the top two songs being given lesser weight so that the figure will reflect the popularity of the album as a whole rather than of one or two successful singles.
The adjusted total is divided by 1000 and added to the album sales figure.
Out of its 41,000 album-equivalent units, 2,900 units came from streaming and the rest were pure sales.
By the end of 2017, The BPI reported that streaming now accounts for over half of music consumption in the UK (50.4%).
In Germany, streaming began to be included on the albums chart since February 2016.
Hence, only paid streaming is counted and must be played at least 30 seconds.
At least 6 tracks of one album have to be streamed to make streams count for the album, with 12 tracks being the maximum counted.
Similar to the UK chart rule, the actual streams of the top-two songs are not counted, but instead the average of the following tracks.
In Forbes, Hugh McIntyre noted that the usage of album equivalent units has made artists release albums with excessive track lists.
Brian Josephs from Spin said: "If you're a thirsty (eager for fame or notoriety) pop artist of note, you can theoretically game the system by packing as many as 20 tracks into an album, in the process rolling up more album-equivalent units—and thus album "sales"—as listeners check the album out."
Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Album-equivalent unit.