Revolutions per minute

Revolutions per minute is a unit of rotational speed for rotating machines.
One revolution per minute is equivalent to hertz.

Standards

A related but distinct quantity for describing rotation is angular frequency, for which the SI unit is the radian per second.
Although they have the same dimensions and base unit, the hertz and radians per second are special names used to express two different but proportional ISQ quantities: frequency and angular frequency, respectively. The conversions between a frequency and an angular frequency are
Thus a disc rotating at 60 rpm is said to have an angular speed of 2π rad/s and a rotation frequency of 1 Hz.
The International System of Units does not recognize rpm as a unit. It defines units of angular frequency and angular velocity as rad s⁻¹, and units of frequency as Hz, equal to s⁻¹.

Examples

For a wheel, a pump, or a crank shaft, the number of times that it completes one full cycle in one minute is given the unit revolution per minute. A revolution is one complete period of motion, whether this be circular, reciprocating or some other periodic motion.
On many kinds of disc recording media, the rotational speed of the medium under the read head is a standard given in rpm. Phonograph records, for example, typically rotate steadily at,, 45 rpm or 78 rpm.
Air turbine rotating up to
Modern air turbine dental drills can rotate at over .
The second hand of a conventional analog clock rotates at 1 rpm.
Audio CD players read their discs at a precise, constant rate and thus must vary the disc's rotational speed from 8 Hz when reading at the innermost edge to 3.5 Hz 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 when reading at the innermost edge, to 10.5 Hz at the outer edge.
A washing machine's drum may rotate at 500 rpm to during the spin cycles.
A baseball thrown by a Major League Baseball pitcher can rotate at over ; faster rotation yields more movement on breaking balls.
A power-generation turbine rotates at 3000 rpm, 3600 rpm, and over 4000 rpm
Modern automobile engines are typically operated around – when cruising, with a minimum speed around 750 rpm – 900 rpm, and an upper limit anywhere from 4800 rpm to up to for a road car, very rarely reaching up to for certain cars, or for racing engines such as those in Formula 1 cars. The exhaust note of V8, V10, and V12 F1 cars has a much higher pitch than an I4 engine, because each of the cylinders 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.
Large two-stroke slow speed diesel engines are often used as ship engines. Most of them operate below 120 rpm, and some very long stroke engines have a maximum speed of around 80 rpm.
A piston aircraft engine typically rotates at a rate between and .
Computer hard drives typically rotate at – , the most common speeds for the ATA or SATA-based drives in consumer models. High-performance drives rotate at – , 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 or even spindle speeds, 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.
Floppy disc drives typically ran at a constant 300 rpm or occasionally 360 rpm 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 were more complex and used variable rotational speeds and per-track storage density to store more data per disc; for example, between 394 rpm and 590 rpm with Mac's 800 kB double-density drive at a constant 39.4 kB/s – versus 300 rpm, 720 kB and 23 kB/s for double-density drives in other machines.
A Zippe-type centrifuge for enriching uranium spins at or faster.
Gas turbine engines rotate at tens of thousands of rpm. JetCat model aircraft turbines are capable of over with the fastest reaching .
A Flywheel energy storage system works at – 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 – on 12 V DC power.
A millisecond pulsar can have near .
A turbocharger can reach , while – is common.
A supercharger can spin at speeds between or as high as –
Molecular microbiology – molecular engines. The rotation rates of bacterial flagella have been measured to be for Salmonella typhimurium, for Escherichia coli, and up to for polar flagellum of Vibrio alginolyticus, allowing the latter organism to move in simulated natural conditions at a maximum speed of 540 mm/h.
The sample in magic angle spinning, a nuclear magnetic resonance technique, typically rotates between and , with experimental instruments reaching speeds as high as .