# Revolutions per minute

Revolutions per minute (rpm, also r/min) is a unit of rotational frequency expressing the number of complete turns a rotating body makes in one minute; it equals one sixtieth of a revolution per second and is widely used for engines, motors, disks, centrifuges, and other rotating machinery even though the SI unit of rotational frequency is the reciprocal second (s⁻¹).<sup>[1](https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-8)</sup><sup> • </sup><sup>[2](https://goldbook.iupac.org/terms/view/R05380/html)</sup>

| | |
|---|---|
| Definition | Rotational frequency n = number of revolutions divided by time interval; SI unit s⁻¹, with r/s and r/min widely used for rotating machinery<sup>[1](https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-8)</sup> |
| Conversions | 1 rpm = 2π/60 rad/s ≈ 0.1047 rad/s = 6 degrees per second = 1/60 Hz<sup>[3](https://sibor.physics.tamu.edu/wp-content/uploads/sites/15/2023/10/chapter9HASversion44-5-4.pdf)</sup><sup> • </sup><sup>[4](https://openstax.org/books/university-physics-volume-1/pages/10-1-rotational-variables)</sup> |
| Standards status | IUPAC lists RPM as a "non-SI unit for rotational frequency" yet its rotational-frequency entry calls rpm "not recommended"<sup>[2](https://goldbook.iupac.org/terms/view/R05380/html)</sup><sup> • </sup><sup>[5](https://goldbook.iupac.org/terms/view/R05412)</sup> |
| Measured value | Tachometers compute RPM = 60 × f[Hz] ÷ PPR (pulses per revolution); hand-held optical units reach about ±0.02–0.05% of reading<sup>[6](https://www.tme.com/us/en-us/news/library-articles/page/75168/tachometer-in-practice-how-it-works-what-it-measures-and-how-to-calibrate-it/)</sup> |
| Machinery range | Wind turbine rotors ~10–20 rpm; car idle 600–1,000 rpm; hard drives up to 15,000 rpm; dental handpieces ~100,000–400,000 rpm<sup>[7](https://whatisrpm.com/machines/typical-rpm-table/)</sup><sup> • </sup><sup>[8](https://www.howtogeek.com/the-weird-story-behind-why-hard-drives-spin-at-such-an-oddly-specific-speeds/)</sup> |
| Centrifugation | RCF (× g) = 1.118 × 10⁻⁵ × R[cm] × S²[rpm]; ultracentrifuge rotors reach 692,149 × g<sup>[9](https://tools.thermofisher.com/content/sfs/brochures/TR0040-Centrifuge-speed.pdf)</sup><sup> • </sup><sup>[10](https://cdn.vanderbilt.edu/vu-web/lab-wpcontent/sites/21/2018/05/21141019/Thermo_Scientific_Rotor_Guide-Exhaustive.pdf)</sup> |
| EV frontier | 2025 announcements above 30,000 rpm (BYD 30,511 rpm, 580 kW); a 50,000 rpm traction-motor prototype has been reported<sup>[11](https://www.pcauto.com/my/news/byd-launches-mass-producible-highest-speed-motor-in-the-world-with-a-maximum-speed-of-30511rpm-15319)</sup><sup> • </sup><sup>[12](https://ousar.lib.okayama-u.ac.jp/files/public/6/69319/20250912092338243791/fulltext.pdf)</sup> |

## Definition and unit status

NIST defines the rotational frequency n of a rotating body as the number of revolutions it makes in a time interval divided by that interval, so the SI unit is the reciprocal second.<sup>[1](https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-8)</sup> Because one revolution is 2π radians, the conversions are exact: 1 rpm = 2π/60 rad/s ≈ 0.1047 rad/s, 1 rpm = 6 degrees per second, and 1 rpm = 1/60 Hz ≈ 0.01667 Hz.<sup>[3](https://sibor.physics.tamu.edu/wp-content/uploads/sites/15/2023/10/chapter9HASversion44-5-4.pdf)</sup><sup> • </sup><sup>[4](https://openstax.org/books/university-physics-volume-1/pages/10-1-rotational-variables)</sup> Conversely, a running speed n in rpm corresponds to a one-per-revolution excitation frequency of n/60 hertz.<sup>[13](https://atlasofengineering.com/mechanical-engineering/critical-speed/)</sup>

The unit's formal standing is stated differently by different bodies, and the difference matters in practice. NIST, following ISO 80000-3, records that the designations "revolutions per second" (r/s) and "revolutions per minute" (r/min) are widely used as units for rotational frequency in specifications on rotating machinery.<sup>[1](https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-8)</sup> IUPAC's dedicated entry defines revolutions per minute (initialism RPM) as a non-SI unit for rotational frequency.<sup>[2](https://goldbook.iupac.org/terms/view/R05380/html)</sup> Yet IUPAC's entry on rotational frequency itself says the synonyms rate of rotation and centrifugation speed, and the traditional units revolutions per minute, r.p.m., rev min⁻¹, and r min⁻¹, are not recommended.<sup>[5](https://goldbook.iupac.org/terms/view/R05412)</sup> rpm is thus simultaneously an accepted non-SI unit and a deprecated notation, depending on which IUPAC entry one reads.

The SI side of the comparison is settled. The 26th CGPM (2019) fixed Hz = s⁻¹ in the redefined SI effective 20 May 2019.<sup>[14](https://www.bipm.org/en/-/resolution-cgpm-26-1)</sup> ISO 80000-3:2019 supplies names, symbols, definitions, and units for quantities of space and time, with conversion factors where appropriate.<sup>[15](https://standards.iteh.ai/catalog/standards/iec/f0b04329-37ca-4e6f-81d6-94adffcb8ed2/iso-80000-3-2019)</sup>

## Physical meaning: frequency, angular velocity, and siblings

Two related quantities describe a spinning shaft. [Rotational frequency](https://www.edgepedia.org/rotational-frequency) counts revolutions per unit time and is expressed in hertz (cycles per second); angular velocity ω measures the rate of change of rotation angle in radians per second.<sup>[4](https://openstax.org/books/university-physics-volume-1/pages/10-1-rotational-variables)</sup> Because frequency and angular frequency have numerical values differing by a factor of 2π, the BIPM advises that any quantity named frequency, angular frequency, or angular velocity be expressed with an explicit unit such as Hz or rad/s rather than a bare s⁻¹, since the reciprocal second by itself leaves it unclear which quantity is intended.<sup>[16](https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf/2d2b50bf-f2b4-9661-f402-5f9d66e4b507?version=1.9)</sup> Ignoring the 2π distinction can therefore produce an error of that factor.<sup>[16](https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf/2d2b50bf-f2b4-9661-f402-5f9d66e4b507?version=1.9)</sup>

Sibling units carve up the same s⁻¹ by context. The hertz is reserved for periodic phenomena and the becquerel for stochastic processes in activity referred to a radionuclide.<sup>[17](https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.330-2019.pdf)</sup> [Angular velocity](https://www.edgepedia.org/angular-velocity) is expressed in radians per second, and multiplying a rotation rate in revolutions per second by 2π gives the angular velocity, since one complete revolution contains 2π radians.<sup>[4](https://openstax.org/books/university-physics-volume-1/pages/10-1-rotational-variables)</sup>

## How rpm is measured

Rotational speed sensors work on three physical principles: conductive tracks, optical reflections, or magnetic field variation; optical and magnetic types are the most common, and magnetic sensing dominates in rough environments such as automotive applications.<sup>[18](https://liu.diva-portal.org/smash/get/diva2:315323/FULLTEXT01)</sup> Hall-effect sensors detect changes in a magnet's field caused by ferromagnetic target material and cover both low-speed and high-speed parts.<sup>[19](https://www.vikacontrols.com.br/wp-content/uploads/2024/05/Catalogo-Solucoes-Istec-para-Velocidade-Bookazine-Speed.v2.pdf)</sup>

**From pulses to rpm.** A tachometer receiving pulses from Hall, variable-reluctance, optical, alternator, or ECU sources computes RPM = 60 × f[Hz] ÷ PPR, where PPR is pulses per revolution.<sup>[6](https://www.tme.com/us/en-us/news/library-articles/page/75168/tachometer-in-practice-how-it-works-what-it-measures-and-how-to-calibrate-it/)</sup> Accuracy improves when the system counts the time between pulses rather than pulses per revolution.<sup>[19](https://www.vikacontrols.com.br/wp-content/uploads/2024/05/Catalogo-Solucoes-Istec-para-Velocidade-Bookazine-Speed.v2.pdf)</sup> Hand-held non-contact optical tachometers typically reach about ±0.02–0.05% of reading, with the best modern non-contact precision solutions about ±0.01%; aeronautical drag-cup eddy-current tachometers may be required to be accurate to about ±4% over a specified range.<sup>[6](https://www.tme.com/us/en-us/news/library-articles/page/75168/tachometer-in-practice-how-it-works-what-it-measures-and-how-to-calibrate-it/)</sup> Commercial specifications quote accuracy as a percentage of reading, for example 0.05% for laser photo units and 0.002–0.001% of setting for stroboscopes.<sup>[20](https://www.sourcebyspec.com/encyclopedia/tachometer.html)</sup>

For aircraft subject to the applicable requirements of 14 CFR 91.205, a tachometer for each engine is required equipment, and an inaccurate tachometer can allow operation beyond the red-line limit, risking catastrophic mechanical failure.<sup>[21](https://aviationtestprep.com/learn/tachometer-types-mechanical-electrical-and-electronic-rpm-indicating-systems)</sup>

## By the numbers

| Machine | Typical speed (rpm) |
|---|---|
| Wind turbine rotor | ~10–20<sup>[7](https://whatisrpm.com/machines/typical-rpm-table/)</sup> |
| Vinyl record | 33⅓, 45, 78 (format standards)<sup>[7](https://whatisrpm.com/machines/typical-rpm-table/)</sup> |
| Washing machine final spin | 1,000–1,600<sup>[7](https://whatisrpm.com/machines/typical-rpm-table/)</sup> |
| Car engine idle / redline | 600–1,000 / 4,000–7,000+<sup>[7](https://whatisrpm.com/machines/typical-rpm-table/)</sup><sup> • </sup><sup>[6](https://www.tme.com/us/en-us/news/library-articles/page/75168/tachometer-in-practice-how-it-works-what-it-measures-and-how-to-calibrate-it/)</sup> |
| Hard drive spindle | 4,200–15,000<sup>[8](https://www.howtogeek.com/the-weird-story-behind-why-hard-drives-spin-at-such-an-oddly-specific-speeds/)</sup> |
| Formula 1 engine (FIA cap) | 15,000<sup>[7](https://whatisrpm.com/machines/typical-rpm-table/)</sup> |
| Automotive turbocharger shaft | ~150,000–300,000<sup>[7](https://whatisrpm.com/machines/typical-rpm-table/)</sup> |
| Dental air-turbine handpiece | ~100,000–400,000<sup>[7](https://whatisrpm.com/machines/typical-rpm-table/)</sup> |

A 15 rpm turbine rotor and a 300,000 rpm turbocharger shaft differ by a factor of 20,000 in the same unit.<sup>[7](https://whatisrpm.com/machines/typical-rpm-table/)</sup> Hard drives standardized on 4,200, 5,400, 7,200, 10,000, and 15,000 rpm, while early disks spun at 1,200, 1,500, and 1,800 rpm; in 2020 [Western Digital](https://www.edgepedia.org/western-digital) marketed "5,400 RPM class" drives that actually spin at 7,200 rpm, so a stated rpm figure may not reflect the real spindle speed.<sup>[8](https://www.howtogeek.com/the-weird-story-behind-why-hard-drives-spin-at-such-an-oddly-specific-speeds/)</sup>

## Rpm in engines and vehicles

A car engine at warm idle typically runs at about 600–1,000 rpm depending on design and condition, and the tachometer's red field marks speeds that threaten drive-unit damage.<sup>[6](https://www.tme.com/us/en-us/news/library-articles/page/75168/tachometer-in-practice-how-it-works-what-it-measures-and-how-to-calibrate-it/)</sup> The redline is a damage limit, not a performance target: in aviation, operating beyond the red-line risks catastrophic mechanical failure.<sup>[21](https://aviationtestprep.com/learn/tachometer-types-mechanical-electrical-and-electronic-rpm-indicating-systems)</sup>

**Electric traction motors** have pushed the frontier upward. [Tesla Model 3](https://www.edgepedia.org/tesla-model-3)/Y motors rotate at about 18,000 rpm and [Porsche Taycan](https://www.edgepedia.org/porsche-taycan) motors reach 25,000 rpm.<sup>[11](https://www.pcauto.com/my/news/byd-launches-mass-producible-highest-speed-motor-in-the-world-with-a-maximum-speed-of-30511rpm-15319)</sup> In 2025, BYD, Xiaomi, and GAC announced EV traction motors exceeding 30,000 rpm; BYD's figure is 30,511 rpm with 580 kW peak power and power density above 16 kW/kg.<sup>[22](https://www.idtechex.com/en/research-article/the-need-for-speed-ev-motors-breaking-the-30-000rpm-barrier/34219)</sup><sup> • </sup><sup>[11](https://www.pcauto.com/my/news/byd-launches-mass-producible-highest-speed-motor-in-the-world-with-a-maximum-speed-of-30511rpm-15319)</sup> The payoff is quantified for radial-flux permanent-magnet machines: raising maximum speed from 10,000 to 20,000 rpm increased power density by 69%, and a further increase to 30,000 rpm gave an additional 41%.<sup>[22](https://www.idtechex.com/en/research-article/the-need-for-speed-ev-motors-breaking-the-30-000rpm-barrier/34219)</sup>

## Rpm in laboratory and industrial equipment

In centrifugation, rpm alone does not describe the separation. The relative centrifugal force is g = (1.118 × 10⁻⁵) R S², where R is the rotor radius in centimeters and S the speed in rpm.<sup>[9](https://tools.thermofisher.com/content/sfs/brochures/TR0040-Centrifuge-speed.pdf)</sup> The same formula appears as RCF (× g) ≈ 1.118 × 10⁻⁵ × r × RPM², and published protocols specify separations in RCF rather than rpm because RCF is the value comparable across different centrifuges and rotors.<sup>[23](https://casrai.org/guides/what-is-a-centrifuge)</sup> The radius dependence is large: 5,000 rpm in a 7 cm-radius microcentrifuge rotor delivers 1,957 × g, while at 14,000 rpm a 7 cm rotor produces 15,339 × g and a 15 cm rotor 32,869 × g.<sup>[9](https://tools.thermofisher.com/content/sfs/brochures/TR0040-Centrifuge-speed.pdf)</sup>

At the top of the range, Thermo Scientific ultracentrifuge rotors list maximum speeds in rpm with corresponding maximum RCF up to 692,149 × g at a maximum radius of 76.5 mm.<sup>[10](https://cdn.vanderbilt.edu/vu-web/lab-wpcontent/sites/21/2018/05/21141019/Thermo_Scientific_Rotor_Guide-Exhaustive.pdf)</sup> Beckman rotors rated at 70,000 rpm show that rotor efficiency depends on both maximum and minimum radius, which together determine the g-force range applied to particles.<sup>[24](https://www.bio.unipd.it/safety/Beckman/data%20sheets/Ultracentrifuge/DS-9721A.pdf)</sup> Benchtop and microcentrifuge models span maximum speeds from 10,200 to 30,000 rpm, some reaching 64,400 × g.<sup>[25](https://media.beckman.com/-/media/pdf-assets/catalogs/centrifugation-product-catalog-benchtop-and-microcentrifuges-2022-06.pdf)</sup> Rotor guides tabulate max speed, max RCF, and k-factor together, which is why rpm alone does not characterize rotor performance.<sup>[10](https://cdn.vanderbilt.edu/vu-web/lab-wpcontent/sites/21/2018/05/21141019/Thermo_Scientific_Rotor_Guide-Exhaustive.pdf)</sup>

## Safe limits and overspeed protection

A critical speed occurs when a running speed or its harmonics coincides with a natural frequency strongly enough to create high vibration. Reaching a critical speed does not by itself mean failure: given enough damping, a quick traverse, and tolerable vibration amplitude, machinery can cross one without harm, though running continuously near a crossing that is lightly damped is considerably riskier.<sup>[13](https://atlasofengineering.com/mechanical-engineering/critical-speed/)</sup>

**Overspeed protection** is quantified in guidelines. An industry guide reports response-time requirements under 40 ms for overspeed protection systems in some current machine guidelines and industry practices.<sup>[19](https://www.vikacontrols.com.br/wp-content/uploads/2024/05/Catalogo-Solucoes-Istec-para-Velocidade-Bookazine-Speed.v2.pdf)</sup> An overspeed detection system (ODS) can continuously measure rotational speed; reaction times and trip limits are set according to applicable IEC and API guidance and OEM specifications, and some systems also monitor acceleration so that a machine losing its load, for example through a broken shaft, may be tripped before reaching the speed limit.<sup>[19](https://www.vikacontrols.com.br/wp-content/uploads/2024/05/Catalogo-Solucoes-Istec-para-Velocidade-Bookazine-Speed.v2.pdf)</sup>

Rotor dynamics set the ceiling in ultra-high-speed motors. A 2025 prototype EV traction motor rated at 50,000 rpm had a measured shaft critical frequency of 1538 Hz and a reported critical rotational speed of 69.5 krpm; the paper gives a safety factor of 1.38 against the maximum speed.<sup>[12](https://ousar.lib.okayama-u.ac.jp/files/public/6/69319/20250912092338243791/fulltext.pdf)</sup>

## Recent developments

The most visible movement is in EV motor speed. Beyond the 2025 announcements above 30,000 rpm from BYD, Xiaomi, and GAC, a 2025 Okayama University paper describes a 50,000 rpm EV traction motor developed from the Hyundai IONIQ5's 15,000 rpm base motor, delivering 160 kW at a 697 V DC bus.<sup>[22](https://www.idtechex.com/en/research-article/the-need-for-speed-ev-motors-breaking-the-30-000rpm-barrier/34219)</sup><sup> • </sup><sup>[12](https://ousar.lib.okayama-u.ac.jp/files/public/6/69319/20250912092338243791/fulltext.pdf)</sup> Outside vehicles, researchers have designed ultra-high-speed permanent magnet motors with integrated rotors reaching 100,000 rpm for hydrogen fuel-vehicle air compression, and built and tested a 25 kW unit.<sup>[26](https://digital-library.theiet.org/doi/full/10.1049/elp2.70100)</sup>

Standards have also moved. IEC 60034-1 edition 15, published 2026, deleted references to IEC TS 60034-25 because converter duty is now defined in clause 3.36, updating the rating and performance standard for rotating electrical machines.<sup>[27](https://webstore.iec.ch/en/publication/112762)</sup> The 2025 edition 2.0 of IEC 60034-30-1 applies to motors from 0.12 kW to 1,000 kW, 50–1,000 V, with 2, 4, 6, or 8 poles on 50 Hz or 60 Hz supplies.<sup>[28](https://webstore.iec.ch/en/publication/91195)</sup> On the unit itself, nothing in the standards landscape has changed: NIST still records r/min as widely used for rotating machinery, and IUPAC's two entries still give rpm dual treatment as a defined non-SI unit and a not-recommended traditional unit.<sup>[1](https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-8)</sup><sup> • </sup><sup>[2](https://goldbook.iupac.org/terms/view/R05380/html)</sup><sup> • </sup><sup>[5](https://goldbook.iupac.org/terms/view/R05412)</sup>

## References

1. [NIST Guide to the SI, Chapter 8](https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-8)
2. [IUPAC Gold Book, revolutions per minute (R05380)](https://goldbook.iupac.org/terms/view/R05380/html)
3. [Chapter 9 Rotational Motion, Texas A&M University course notes](https://sibor.physics.tamu.edu/wp-content/uploads/sites/15/2023/10/chapter9HASversion44-5-4.pdf)
4. [10.1 Rotational Variables, University Physics Volume 1, OpenStax](https://openstax.org/books/university-physics-volume-1/pages/10-1-rotational-variables)
5. [IUPAC Gold Book, rotational frequency (R05412)](https://goldbook.iupac.org/terms/view/R05412)
6. [Tachometer in practice, Transfer Multisort Elektronik technical library](https://www.tme.com/us/en-us/news/library-articles/page/75168/tachometer-in-practice-how-it-works-what-it-measures-and-how-to-calibrate-it/)
7. [Typical RPM Table: From Wind Turbines to Dental Drills, whatisrpm.com](https://whatisrpm.com/machines/typical-rpm-table/)
8. [The weird story behind why hard drives spin at such oddly specific speeds, How-To Geek](https://www.howtogeek.com/the-weird-story-behind-why-hard-drives-spin-at-such-an-oddly-specific-speeds/)
9. [Tech Tip #40: Converting RPM to RCF, Thermo Fisher Scientific](https://tools.thermofisher.com/content/sfs/brochures/TR0040-Centrifuge-speed.pdf)
10. [Thermo Scientific Rotor Guide](https://cdn.vanderbilt.edu/vu-web/lab-wpcontent/sites/21/2018/05/21141019/Thermo_Scientific_Rotor_Guide-Exhaustive.pdf)
11. [BYD Launches Mass-Producible Highest-Speed Motor With a Maximum Speed of 30511RPM, pcauto.com](https://www.pcauto.com/my/news/byd-launches-mass-producible-highest-speed-motor-in-the-world-with-a-maximum-speed-of-30511rpm-15319)
12. [Development of 50 krpm Ultra-High Speed IPMSM for EV Traction, Okayama University repository](https://ousar.lib.okayama-u.ac.jp/files/public/6/69319/20250912092338243791/fulltext.pdf)
13. [Critical Speed in Rotating Machinery, Atlas of Engineering](https://atlasofengineering.com/mechanical-engineering/critical-speed/)
14. [Resolution 1 of the 26th CGPM (2019), BIPM](https://www.bipm.org/en/-/resolution-cgpm-26-1)
15. [ISO 80000-3:2019, Quantities and units, Space and time](https://standards.iteh.ai/catalog/standards/iec/f0b04329-37ca-4e6f-81d6-94adffcb8ed2/iso-80000-3-2019)
16. [The International System of Units (SI Brochure, 9th edition), BIPM](https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf/2d2b50bf-f2b4-9661-f402-5f9d66e4b507?version=1.9)
17. [The International System of Units (SI), 2019 Edition, NIST SP 330](https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.330-2019.pdf)
18. [Rotational Speed Sensors: Limitations, Pre-processing and Automotive Applications, Linköping University thesis](https://liu.diva-portal.org/smash/get/diva2:315323/FULLTEXT01)
19. [SPEED, Istec speed measurement and overspeed protection bookazine](https://www.vikacontrols.com.br/wp-content/uploads/2024/05/Catalogo-Solucoes-Istec-para-Velocidade-Bookazine-Speed.v2.pdf)
20. [Tachometer Guide, Types, Specs, Selection, Source by Spec](https://www.sourcebyspec.com/encyclopedia/tachometer.html)
21. [Tachometer Types: Mechanical, Electrical, and Electronic RPM Indicating Systems, Aviation Test Prep](https://aviationtestprep.com/learn/tachometer-types-mechanical-electrical-and-electronic-rpm-indicating-systems)
22. [The Need for Speed: EV Motors Breaking the 30,000rpm Barrier, IDTechEx](https://www.idtechex.com/en/research-article/the-need-for-speed-ev-motors-breaking-the-30-000rpm-barrier/34219)
23. [What Is a Centrifuge? Types, RCF vs. RPM, and Common Lab Uses, CASRAI](https://casrai.org/guides/what-is-a-centrifuge)
24. [Comparative Efficiencies of Two 70,000 rpm Rotors, Beckman data sheet DS-9721A](https://www.bio.unipd.it/safety/Beckman/data%20sheets/Ultracentrifuge/DS-9721A.pdf)
25. [Beckman Coulter Centrifugation Product Catalog, Benchtop and Microcentrifuges (2022-06)](https://media.beckman.com/-/media/pdf-assets/catalogs/centrifugation-product-catalog-benchtop-and-microcentrifuges-2022-06.pdf)
26. [Design and Multi-Physics Field Analysis of an Ultra High Speed PMSM With Integrated Rotor, IET Electric Power Applications](https://digital-library.theiet.org/doi/full/10.1049/elp2.70100)
27. [IEC 60034-1:2026 RLV, Rotating electrical machines, Part 1: Rating and performance](https://webstore.iec.ch/en/publication/112762)
28. [IEC 60034-30-1:2025, Rotating electrical machines, Part 30-1: Efficiency classes](https://webstore.iec.ch/en/publication/91195)

---
*Topic: Encyclopedia › Physical world and mathematics › Measurement and time › Units and unit systems › Units by physical quantity › Units of frequency, rotation, and temporal rates*

*Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 15, 2026 · Edited: Sep 30, 2026; Oct 15, 2026 · Last review: Oct 15, 2026*

*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*

License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license