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 80000-3:2019 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 The superseded standard ISO 80000-3:2006 did however state with reference to the unit name 'one', symbol '1', that "The special name revolution, symbol r, for this unit is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 ...
,
Hz, as equal to s
−1.
:
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:
:
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 drills 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 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 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'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 ...
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 balls.
*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.
* 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 regarded ...
engine
An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.
Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ...
s 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 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 cars 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
A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base.
A cylinder may also be defined as an infini ...
of a
four-stroke engine 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 adapter, 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) ...
-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
Fibre Channel (FC) is a high-speed data transfer protocol providing in-order, lossless delivery of raw block data. Fibre Channel is primarily used to connect computer data storage to servers in storage area networks (SAN) in commercial data c ...
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 drive
A solid-state drive (SSD) is a solid-state storage device that uses integrated circuit assemblies to store data persistently, typically using flash memory, and functioning as secondary storage in the hierarchy of computer storage. It i ...
s 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 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 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 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 pr ...
can reach 290,000 rpm (4.8 kHz), while 80,000–200,000 rpm (1–3 kHz) is common.
* A
supercharger
In an internal combustion engine, a supercharger compresses the intake gas, forcing more air into the engine in order to produce more power for a given displacement.
The current categorisation is that a supercharger is a form of forced indu ...
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'', 16,200 rpm (270 Hz) for ''
Escherichia coli
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...
'', 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 (CAV) – used when referring to the speed of gramophone (phonograph) records
*
Constant linear velocity (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)
*
Idle speed
*
Overspeed (engine)
Overspeed is a condition in which an engine is allowed or forced to turn beyond its design limit. The consequences of running an engine too fast vary by engine type and model and depend upon several factors, the most important of which are the du ...
*
Redline
*
Rev limiter
References
{{reflist
Units of frequency
Units of angular velocity