Revolutions per minute

Revolutions per minute

Revolutions per minute (abbreviated rpm, RPM, r/min, or r·min−1) 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::3600 r/min = 60 revolutions per second = 60 Hz

In the SI one often uses the unit for angular velocity which is radians per second (rad·s−1)::1 r/min = 2π rad·min−1 = 2π/60 rad·s−1 ≈ 0.10471976 rad·s−1

To convert revolutions per minute to revolutions per second (hertz), one simply divides by 60. The opposite is true when converting from hertz to RPM, where one multiplies by 60 instead.


* 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 2/3, 33⅓, 45 or 78 r/min (⁴⁄₁₅, ⁵⁄₉, ³⁄₄, or 1.3 Hz).
* Modern ultrasonic dental drills can rotate at up to 800,000 r/min (10 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.cite web
title= "Physical parameters of DVD"
accessdate= 2008-05-30
date= 1996-07-21
work= DVD Technical Notes
publisher= Moving Picture Experts Group (MPEG)
] 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 usually given in multiples of this figure.
* A washing machine's drum may rotate at 500 to 2000 r/min (8–33 Hz) during the spin cycles.
* An automobile's engine typically varies between 700 and 7000 r/min (12–120 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 (30–50 Hz).
* Computers’ hard drives typically rotate at 5400 or 7200 r/min (90 or 120 Hz)—most commonly with ATA or SATA interfaces—and 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. [cite web|url=|title=The Official Formula 1 Website||accessdate=2008-05-13]
* A Zippe-type centrifuge for enriching uranium spins at 90,000 r/min (1,500 Hz) or faster. [cite web|url=|title=Slender and Elegant, It Fuels the Bomb||accessdate=2006-09-24]
* 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). [cite web|url=| title=JetCat P-60 turbine specification page||accessdate=2006-07-19]

* An electromechanical battery (EMB) works at 60,000–200,000 r/min (1–3 kHz) range using a passively magnetic levitated flywheel in vacuum. [Citation
last = Post
first = Richard F.
publication-date = April 1996
year = 1996
title = A New Look at an Old Idea: The Electromechanical Battery
periodical = Science & Technology Review
publication-place = Livermore, CA
publisher = University of California, Lawrence Livermore National Laboratory
pages = 12-19
id = ISSN: 10923055
url =
accessdate = 2008-05-30
] 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 80,000–200,000 r/min (1–3 kHz) is common.

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