Revolutions per minute
Revolutions per minute (abbreviated rpm, RPM, r/min, or rmin1) is a unit of frequency: the number of full rotations completed in one minute around a fixed axis. It is most commonly used as a measure of rotational speed or angular velocity of some mechanical component.
Standards organizations generally recommend the symbol r/min, which is more consistent with the general use of unit symbols. This is not enforced as an international standard; in French, for example, tr/mn (tours par minute) is commonly used.
The corresponding International System of Units (SI) unit would be the hertz and we have:
In the SI one often uses the unit for angular velocity which is radians per second (rads1):
To convert revolutions per minute to revolutions per second (hertz), simply divide by 60.

# Examples
- On some kinds of disc or tape-like recording media, the rotational speed of the medium under the read head is a standard given in r/min. Gramophone (phonograph) records, for example, typically rotate steadily at 16, 3313, 45 or 78 r/min (415, 59, 34, or 1.3 Hz).
- Modern dental drills can rotate at up to 500,000 r/min (8 kHz).
- The second hand of a conventional analogue clock rotates at 1 r/min.
- Audio CD players read their discs at a constant 150 kB/s and thus must vary the disc's rotational speed from around 500 r/min (actually 8 Hz), when reading at the innermost edge, to 200 r/min (actually 3.5 Hz) at the outer edge. CD-ROM drives maximum rotational speeds are rated in multiples of this figure, even though they do not hold to constant read speeds when reading from most disc formats.
- DVD players also usually read discs at a constant linear rate. The disc's rotational speed varies from 1530 r/min (actually 25.5 Hz), when reading at the innermost edge, and 630 r/min (actually 10.5 Hz) at the outer edge. DVD drives speeds are are usually given in multiples of this figure.
- A washing machine's drum may rotate at 500 to 2000 r/min (833 Hz) during the spin cycles.
- An automobile's engine typically varies between 700 and 7000 r/min (12120 Hz) though some cars engines can spin as quickly as 11,000 r/min (180 Hz).
- A piston aircraft engine typically rotates at a rate between 2000 and 3000 r/min (3050 Hz).
- Computers hard drives typically rotate at 5400 or 7200 r/min (90 or 120 Hz)most commonly with ATA or SATA interfacesand some high-performance drives rotate at 10,000 or 15,000 r/min (160 or 250 Hz)usually with SATA, SCSI or Fibre Channel interfaces.
- The engine of a Formula One racing car can reach 19,000 r/min (320 Hz) under some circumstances.
- A Zippe-type centrifuge for enriching uranium spins at 90,000 r/min (1,500 Hz) or faster.
- Gas turbine engines rotate at tens of thousands of r/min. JetCat model aircraft turbines are capable of over 100,000 r/min (1,700 Hz) with the fastest reaching 165,000 r/min (2,750 Hz).
- An electromechanical battery (EMB) works at 60,000200,000 r/min (13 kHz) range using a passively magnetic levitated flywheel in vacuum. The choice of the flywheel material is not the most dense, but the one that pulverises the most safely, at surface speeds about 7 times the speed of sound.
- A turbocharger can reach 290,000 r/min (4,800 Hz), while 80,000200,000 r/min (13 kHz) is common.