beat per minute

The beat per minute is the one frequency unit shared by musicians, cardiologists and running watches, and each field occupies its own stretch of the scale. Music mostly lives between 60 and 180 bpm, with house near 125 and drum and bass near 174; distance-running coaches push cadence toward 180 steps per minute; and biology brackets everything, from a diving blue whale's heart slowing toward 2 bpm up to a hummingbird's passing 1,200 in flight.

The initials attached to printed tempos name a machine and its promoter. Classical scores read "M.M. ♩ = 120", where M.M. stands for Maelzel's Metronome: Johann Maelzel patented the clockwork metronome in 1815, and Beethoven, an early adopter, published metronome figures for his first eight symphonies in 1817, marks conductors still argue about because many seem implausibly fast.

Converting is one division: bpm over 60 is hertz, so 120 bpm is exactly 2 Hz with a period of half a second, which is how the frequency type on this site will hand it back. The period view is the practical one in studios, where delay effects are set from the tempo: an eighth-note echo at 120 bpm is 250 ms, and every delay pedal with a tap-tempo button is doing this page's conversion live.