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Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of
rotational speed Rotational frequency (also known as rotational speed or rate of rotation) of an object rotating around an axis is the frequency of rotation of the object. Its unit is revolution per minute (rpm), cycle per second (cps), etc. The symbol fo ...
or rotational frequency for rotating machines.


Standards

ISO 80000-3 ISO 80000 or IEC 80000 is an international standard introducing the International System of Quantities (ISQ). It was developed and promulgated jointly by the International Organization for Standardization (ISO) and the International Electrotech ...
:2019 defines a unit of rotation as the dimensionless unit equal to 1, which it refers to as a revolution, but does not define the revolution as a unit. It defines a unit of rotational frequency equal to s−1. The superseded standard ISO 80000-3:2006 did however state with reference to the unit name 'one', symbol '1', that "The special name revolution, symbol r, for this unit is widely used in specifications on rotating machines." The International System of Units (SI) does not recognize rpm as a unit, and defines the unit of
frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
, Hz, as equal to s−1. :\begin 1~&\text &&=& 60~&\text \\ \frac~&\text &&=& 1~&\text \end A corresponding but distinct quantity for describing rotation is angular velocity, for which the SI unit is the radian per second. Although they have the same dimensions (s−1), hertz (Hz) and radian per second (rad/s) are two different units and are used to measure two different but proportional ISQ quantities: frequency and angular frequency (angular speed, magnitude of angular velocity) respectively. The conversions between a frequency and an angular velocity are: :\omega = 2 \pi f\,, \qquad f = \frac \,. Thus a disc rotating at 60 rpm is said to be have an angular speed of 2''π'' rad/s and a rotation frequency of 1 Hz.


Examples

*On many kinds of disc recording media, the rotational speed of the medium under the read head is a standard given in rpm. Phonograph (gramophone) records, for example, typically rotate steadily at , , 45 or 78 rpm (0.28, 0.55, 0.75, or 1.3 Hz respectively). *Modern air turbine
dental drill A dental drill or handpiece is a hand-held, mechanical instrument used to perform a variety of common dental procedures, including removing decay, polishing fillings, performing cosmetic dentistry, and altering prostheses. The handpiece itse ...
s can rotate at up to 800,000 rpm (13.3 kHz). *The second hand of a conventional analog clock rotates at 1 rpm. *
Audio CD Compact Disc Digital Audio (CDDA or CD-DA), also known as Digital Audio Compact Disc or simply as Audio CD, is the standard format for audio compact discs. The standard is defined in the ''Red Book'', one of a series of Rainbow Books (named ...
players read their discs at a precise, constant rate (4.3218 Mbit/s of raw physical data for 1.4112 Mbit/s (176.4 kB/s) of usable audio data) and thus must vary the disc's rotational speed from 8 Hz (480 rpm) when reading at the innermost edge, to 3.5 Hz (210 rpm) at the outer edge. *
DVD The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any kind ...
players also usually read discs at a constant linear rate. The disc's rotational speed varies from 25.5 Hz (1530 rpm) when reading at the innermost edge, to 10.5 Hz (630 rpm) at the outer edge. *A
washing machine A washing machine (laundry machine, clothes washer, washer, or simply wash) is a home appliance used to wash laundry. The term is mostly applied to machines that use water as opposed to dry cleaning (which uses alternative cleaning fluids and ...
's drum may rotate at 500 to 2,000 rpm (8–33 Hz) during the spin cycles. *A
baseball Baseball is a bat-and-ball sport played between two teams of nine players each, taking turns batting and fielding. The game occurs over the course of several plays, with each play generally beginning when a player on the fielding t ...
thrown by a
Major League Baseball Major League Baseball (MLB) is a professional baseball organization and the oldest major professional sports league in the world. MLB is composed of 30 total teams, divided equally between the National League (NL) and the American League (AL), ...
pitcher can rotate at over 2,500 rpm (41.7 Hz); faster rotation yields more movement on
breaking ball In baseball, a breaking ball is a pitch that does not travel straight as it approaches the batter; it will have sideways or downward motion on it, sometimes both (see slider). A breaking ball is not a specific pitch by that name, but is any ...
s. *A power generation turbine ( with a two-pole alternator) rotates at 3000 rpm (50 Hz) or 3600 rpm (60 Hz), depending on country – see
AC power plugs and sockets AC power plugs and sockets connect electric equipment to the alternating current (AC) mains electricity power supply in buildings and at other sites. Electrical plugs and sockets differ from one another in voltage and electric current, current ...
. * Modern
automobile A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarde ...
engines are typically operated around 2,000–3,000 rpm (33–50 Hz) when cruising, with a minimum (idle) speed around 750–900 rpm (12.5–15 Hz), and an upper limit anywhere from 4500 to 10,000 rpm (75–166 Hz) for a road car, very rarely reaching up to 12,000 rpm for certain cars (such as the GMA T.50), or 20,000 rpm for racing engines such as those in Formula 1 cars (during the season, with the 2.4 L N/A
V8 engine A V8 engine is an eight-cylinder piston engine in which two banks of four cylinders share a common crankshaft and are arranged in a V configuration. The first V8 engine was produced by the French Antoinette company in 1904, developed and u ...
configuration; limited to 15,000 rpm, with the 1.6 L V6 turbo- hybrid engine configuration). The exhaust note of V8, V10, and V12
F1 car A Formula One car (also known as an F1 car) is a single-seat, open-cockpit, open-wheel formula racing car with substantial front and rear wings, and an engine positioned behind the driver, intended to be used in competition at Formul ...
s has a much higher pitch than an
I4 engine A straight-four engine (also called an inline-four) is a four-cylinder piston engine where cylinders are arranged in a line along a common crankshaft. The vast majority of automotive four-cylinder engines use a straight-four layout (with the e ...
, because each of the cylinders of a
four-stroke engine A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either directi ...
fires once for every two revolutions of the crankshaft. Thus an eight-cylinder engine turning 300 times per second will have an exhaust note of 1,200 Hz. *A piston aircraft engine typically rotates at a rate between 2,000 and 3,000 rpm (30–50 Hz). *Computer hard drives typically rotate at 5,400 or 7,200 rpm (90 or 120 Hz), the most common speeds for the ATA or
SATA SATA (Serial AT Attachment) is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. Serial ATA succeeded the earlier Parallel ATA (PATA) standard t ...
-based drives in consumer models. High-performance drives (used in fileservers and enthusiast-gaming PCs) rotate at 10,000 or 15,000 rpm (160 or 250 Hz), usually with higher-level SATA, SCSI or Fibre Channel interfaces and smaller platters to allow these higher speeds, the reduction in storage capacity and ultimate outer-edge speed paying off in much quicker access time and average transfer speed thanks to the high spin rate. Until recently, lower-end and power-efficient laptop drives could be found with 4,200 or even 3,600 rpm spindle speeds (70 and 60 Hz), but these have fallen out of favour due to their lower performance, improvements in energy efficiency in faster models and the takeup of solid-state drives for use in slimline and ultraportable laptops. Similar to CD and DVD media, the amount of data that can be stored or read for each turn of the disc is greater at the outer edge than near the spindle; however, hard drives keep a constant rotational speed so the effective data rate is faster at the edge (conventionally, the "start" of the disc, opposite to a CD or DVD). * Floppy disc drives typically ran at a constant 300 or occasionally 360 rpm (a relatively slow 5 or 6 Hz) with a constant per-revolution data density, which was simple and inexpensive to implement, though inefficient. Some designs such as those used with older Apple computers (Lisa, early Macintosh, later II's) were more complex and used variable rotational speeds and per-track storage density (at a constant read/record rate) to store more data per disc; for example, between 394 rpm (with 12 sectors per track) and 590 rpm (8 sectors) with Mac's 800 KB double-density drive at a constant 39.4 kB/s (max) – versus 300 rpm, 720 KB and 23 kB/s (max) for double-density drives in other machines. *A Zippe-type centrifuge for enriching uranium spins at 90,000 rpm (1,500 Hz) or faster. *
Gas turbine A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directio ...
engines rotate at tens of thousands of rpm. JetCat model aircraft turbines are capable of over 100,000 rpm (1,700 Hz) with the fastest reaching 165,000 rpm (2,750 Hz). *A
Flywheel energy storage Flywheel energy storage (FES) works by accelerating a rotor (flywheel) to a very high speed and maintaining the energy in the system as rotational energy. When energy is extracted from the system, the flywheel's rotational speed is reduced as a c ...
system works at 60,000–200,000 rpm (1–3 kHz) range using a passively magnetic levitated flywheel in a 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 typical 80 mm, 30 CFM computer fan will spin at 2,600–3,000 rpm (43–50 Hz) on 12-V DC power. *A
millisecond pulsar A millisecond pulsar (MSP) is a pulsar with a rotational period less than about 10 milliseconds. Millisecond pulsars have been detected in radio, X-ray, and gamma ray portions of the electromagnetic spectrum. The leading theory for the origin of ...
can have near 50,000 rpm (833 Hz). *A
turbocharger In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...
can reach 290,000 rpm (4.8 kHz), while 80,000–200,000 rpm (1–3 kHz) is common. * A supercharger can spin at speeds between or as high as 50,000-65,000 rpm (833–1083 Hz) *Molecular microbiology – molecular engines. The rotation rates of bacterial flagella have been measured to be 10,200 rpm (170 Hz) for ''
Salmonella typhimurium ''Salmonella enterica'' subsp. ''enterica'' is a subspecies of ''Salmonella enterica'', the rod-shaped, flagellated, aerobic, Gram-negative bacterium. Many of the pathogenic serovars of the ''S. enterica'' species are in this subspecies, includin ...
'', 16,200 rpm (270 Hz) for '' Escherichia coli'', and up to 102,000 rpm (1,700 Hz) for polar flagellum of '' Vibrio alginolyticus'', allowing the latter organism to move in simulated natural conditions at a maximum speed of 540 mm/h.


See also

*
Constant angular velocity In optical storage, constant angular velocity (CAV) is a qualifier for the rated speed of any disc containing information, and may also be applied to the writing speed of recordable discs. A drive or disc operating in CAV mode maintains a cons ...
(CAV) – used when referring to the speed of gramophone (phonograph) records *
Constant linear velocity In optical storage, constant linear velocity (CLV) is a qualifier for the rated speed of an optical disc drive, and may also be applied to the writing speed of recordable discs. CLV implies that the angular velocity (i.e. rpm) varies during an ...
(CLV) – used when referring to the speed of audio CDs * Radian per second *
Rotational speed Rotational frequency (also known as rotational speed or rate of rotation) of an object rotating around an axis is the frequency of rotation of the object. Its unit is revolution per minute (rpm), cycle per second (cps), etc. The symbol fo ...
* Compressor map *
Turn (geometry) A turn is a unit of plane angle measurement equal to  radians, 360  degrees or 400  gradians. Subdivisions of a turn include half-turns, quarter-turns, centiturns, milliturns, etc. The closely related terms ''cycle'' and ''rev ...
*
Idle speed Idling refers to running a vehicle's engine when the vehicle is not in motion. This commonly occurs when drivers are stopped at a red light, waiting while parked outside a business or residence, or otherwise stationary with the engine running. Wh ...
* Overspeed (engine) * Redline * Rev limiter


References

{{reflist Units of frequency Units of angular velocity