"21 Seconds" is a song by the UK garage act So Solid Crew. It is included on their debut album They Don't Know. The song was released as a single on Relentless Records in 2001. It charted at a peak position of number one in the UK Singles Chart in August 2001, while it peaked just outside the top 40 in the Netherlands. It achieved first week sales of 118,135 units in the United Kingdom. The full album version features So Solid Crew members in the following order: Megaman, Asher D, Mac, Kaish, G-Man, Harvey, Romeo, Lisa Maffia, Face & Skatt D. The single version places Harvey's, Romeo's & Lisa Maffia's raps after Face & Skatt D's raps. The chorus is sung by Kaish.
The song title alludes to the approximate 21 seconds that each of the band members is given to perform their rap. 21 seconds is arrived at as the song's tempo is approximately 140BPM and each rapper has 12 bars of 4 beats (48 beats at 140BPM, when worked out to the nearest integer, rounds to 21 seconds).