Frequency Converters — Hz, kHz, MHz, GHz
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Frequency conversions span four dominant units that together cover every modern radio-communication, audio-engineering, computing-clock-rate, and electromagnetic-spectrum specification across the 1 Hz to 100 GHz range. The hertz (Hz) is the SI-derived primary frequency unit equal to one cycle per second, named at the 14th CGPM in 1971 to honour Heinrich Hertz's 1886-1889 demonstration of electromagnetic waves. The kilohertz (kHz, 1000 Hz) dominates AM radio broadcasting (535-1605 kHz medium-wave), audio sampling rates (44.1-192 kHz), audio-equipment frequency response (up to 20 kHz human hearing), and low-frequency ultrasound. The megahertz (MHz, 10⁶ Hz) dominates FM radio (88-108 MHz), TV broadcasting (470-694 MHz UHF), legacy CPU clocks (1-1000 MHz era 1980s-1990s), medical ultrasound (1-15 MHz), and amateur radio bands. The gigahertz (GHz, 10⁹ Hz) dominates modern computing CPU clock-rates (3-5 GHz peak boost), mobile-cellular communication (0.6-6 GHz mid-band, 24-39 GHz mmWave 5G), WiFi (2.4, 5, 6 GHz), and satellite-communication (1-40 GHz across L through Ka bands). The four units coexist across cross-disciplinary contexts where audio-engineering, radio-communication, computing-clock-rate specification, and SI-canonical scientific publication all need parallel frequency-unit reference frameworks anchored to the SI second. Modern atomic-clock metrology at 9.192631770 GHz Cs-133 hyperfine-transition primary standards and emerging optical-lattice atomic clocks at hundreds of THz approach 1 part in 10^18 precision at the current frontier of national-metrology-institute primary timekeeping infrastructure.
Units in this category
Hertz (Hz)
The hertz (Hz) is the SI-derived unit of frequency, equal to one cycle, oscillation, or event per second of time (1 Hz = 1/s). The hertz is anchored to the SI second via the 1967 atomic-clock definition (Cs-133 hyperfine-transition at exactly 9,192,631,770 Hz). Higher-frequency multiples use kilohertz (kHz, 10³ Hz), megahertz (MHz, 10⁶ Hz), gigahertz (GHz, 10⁹ Hz), terahertz (THz, 10¹² Hz), and petahertz (PHz, 10¹⁵ Hz).
Kilohertz (kHz)
The kilohertz (kHz) is exactly 1000 hertz by SI prefix definition. The relationship is fixed and exact, with the kilo- prefix denoting 1000 of the underlying unit. One kHz equals 1000 cycles per second.
Megahertz (MHz)
The megahertz (MHz) is exactly 1,000,000 hertz (10⁶ Hz) by SI prefix definition. The relationship is fixed and exact, with the mega- prefix denoting 10⁶ of the underlying unit. One MHz equals 1,000,000 cycles per second.
Gigahertz (GHz)
The gigahertz (GHz) is exactly 1,000,000,000 hertz (10⁹ Hz) by SI prefix definition. The relationship is fixed and exact, with the giga- prefix denoting 10⁹ of the underlying unit. One GHz equals 1 billion cycles per second.
History of frequency measurement
Frequency measurement traces from Heinrich Hertz's 1886-1889 experiments at the University of Karlsruhe demonstrating electromagnetic-wave propagation through twentieth-century radio-and-television-broadcasting standardisation. Hertz's spark-gap transmitters and resonant-loop receivers operated at frequencies around 50-500 MHz, anticipating by decades the radio-and-television-broadcast frequency landscape that would emerge through the twentieth century. The unit "hertz" was formally adopted at the 14th CGPM in 1971 to name the SI-derived unit of frequency. Radio-and-TV-broadcasting standardised on kHz, MHz allocations through twentieth-century ITU radio-regulation development, with the modern global frequency-band landscape established by mid-twentieth-century international agreements. Computing CPU clock-rates transitioned from kHz (1970s mainframe-era) to MHz (1980s-1990s personal computer era) to GHz (since 2000 with the Pentium 4 launch at 1.5 GHz). The 2019 SI redefinition preserved the hertz definition as a derived unit anchored through the SI second to the Cs-133 hyperfine-transition atomic-clock primary standard at exactly 9.192631770 GHz. The frequency unit hierarchy from Hz through GHz to THz now spans fifteen orders of magnitude across audio, radio, computing, and atomic-spectroscopy applications globally with exact integer-prefix relationships throughout the SI system.
Where frequency conversions matter
Frequency conversions appear across every modern radio, audio, computing, and electromagnetic-spectrum context. Radio communication globally uses kHz for AM (535-1605 kHz medium-wave, 153-279 kHz long-wave), MHz for FM (88-108 MHz) and TV (470-694 MHz UHF) broadcasting, and GHz for mobile-cellular (0.6-6 GHz sub-6, 24-39 GHz mmWave 5G), WiFi (2.4, 5, 6 GHz WiFi 6E), and satellite-communication (Ku-band 12-18 GHz, Ka-band 26-40 GHz). Audio engineering uses Hz/kHz universally for human-hearing (20 Hz-20 kHz) and audio-equipment frequency response specifications, audio sampling rates (44.1 kHz CD, 48 kHz video, 96-192 kHz hi-res), and audio-and-music production equipment. Computing CPU clock-rates use GHz universally on every modern CPU consumer-marketing material and engineering spec (typical desktop and laptop CPUs at 3-5 GHz peak boost). RAM clock-speeds use MHz and GHz (DDR4 at 1.6-3.2 GHz effective, DDR5 at 4-8 GHz effective). Electric-power-grid frequency at 50 Hz (EU, UK, Asia outside Japan, Australia, Latin America, Africa) or 60 Hz (US, Canada, Mexico, Japan in part) is critical for synchronous-generator coordination. Medical ultrasound uses MHz (1-15 MHz clinical imaging, 20 kHz to MHz physiotherapy and industrial cleaning). Atomic-clock metrology uses GHz for the Cs-133 hyperfine-transition at 9.192631770 GHz primary standard, with optical-lattice atomic clocks at hundreds of THz approaching 1 part in 10^18 precision.
How to convert frequency units
Frequency-unit conversion runs against the SI hertz as the primary reference, with each prefix-multiple related to the hertz by exact integer factors: 1 kHz = 1000 Hz exactly, 1 MHz = 1,000,000 Hz = 1000 kHz exactly, 1 GHz = 1,000,000,000 Hz = 1000 MHz = 1,000,000 kHz exactly. The factors are exact since the SI prefix system fixes them as exact integer multiples. Cross-conversion between prefix-multiples uses the directly-tabulated factors: 1 GHz = 1000 MHz = 1,000,000 kHz; 1 MHz = 1000 kHz = 1,000,000 Hz. The case-sensitive prefix distinction is critical: "kHz" (kilo-, 1000) versus "kHz" (no other interpretation), "MHz" (mega-, 10⁶) versus "mHz" (milli-, 10⁻³, a billion-fold difference). The conversion runs at every cross-context audio-radio-computing-and-spectroscopy boundary, with the natural unit-scale appropriate for each application: Hz for power-grid frequency and audio low-frequency; kHz for audio mid-range and AM radio; MHz for FM radio, TV, and medical ultrasound; GHz for CPU clock-rates, mobile-cellular, WiFi, and satellite communication.
All frequency conversions
Frequently asked questions
How many Hz in 1 kHz?
One kilohertz equals exactly 1000 hertz by SI prefix definition. The thousandfold ratio is fixed by the SI prefix system and is exact across every modern frequency-measurement context. The "1 kHz = 1000 Hz" reference is the canonical audio-engineering and AM-radio frequency-conversion factor.
How many kHz in 1 MHz?
One megahertz equals exactly 1000 kilohertz (1,000,000 Hz) by SI prefix definition. The thousandfold ratio between MHz and kHz follows from the SI prefix system. The conversion is exact, and the "1 MHz = 1000 kHz" reference appears in radio-frequency engineering across AM-vs-FM frequency-band cross-references and audio-vs-radio frequency comparisons.
How many MHz in 1 GHz?
One gigahertz equals exactly 1000 megahertz (1,000,000,000 Hz = 1 billion Hz) by SI prefix definition. The thousandfold ratio between GHz and MHz follows from the SI prefix system. The conversion is exact, and the "1 GHz = 1000 MHz" reference is the canonical CPU-clock-rate, mobile-cellular, and WiFi frequency-conversion factor.
Why does the US power grid use 60 Hz but the EU uses 50 Hz?
The 60 Hz US standard emerged from late-nineteenth-century AC-power-system development at Westinghouse Electric and General Electric, with 60 Hz chosen as the optimal trade-off between synchronous-motor performance and AC-transformer efficiency. The 50 Hz European standard was adopted by AEG in Germany in the 1890s and spread across continental Europe with similar efficiency-and-performance optimisation considerations. The two frequencies have remained stable as regional standards since, with the 50/60 Hz split now an entrenched feature of global electric-power-grid infrastructure.
Why is the Cs-133 atomic-clock frequency 9.192 GHz?
The 1967 SI second-redefinition fixed the second as exactly 9,192,631,770 periods of the Cs-133 hyperfine-transition radiation, equivalent to a 9.192631770 GHz frequency. The figure was measured experimentally before the redefinition and chosen as the SI second-anchor because the Cs-133 hyperfine transition is a stable, reproducible quantum-mechanical transition that primary atomic-clock standards (caesium-fountain clocks) at NIST, NPL, PTB, NMIJ can measure to better than 1 part in 10^15 precision.
How does WiFi frequency relate to mobile-cellular?
WiFi operates in unlicensed bands at 2.4 GHz (802.11b/g/n), 5 GHz (802.11a/n/ac/ax), and 6 GHz (802.11ax WiFi 6E). Mobile-cellular operates in licensed bands across 0.6-6 GHz (sub-6 GHz 4G LTE and 5G NR) and 24-39 GHz (mmWave 5G). The two coexist in adjacent spectrum allocations under ITU radio regulations, with WiFi using unlicensed lower-power local-area coverage and mobile-cellular using licensed higher-power wide-area coverage.
How does CD-audio sample rate relate to human hearing?
CD-audio uses 44.1 kHz sampling rate, established by Sony and Philips in the 1980 Red Book CD audio specification. The figure is sufficient to capture human-hearing's 20 kHz upper limit under the Nyquist-Shannon sampling theorem, which requires sampling at greater than twice the highest frequency to be captured (so 44.1 kHz captures up to 22.05 kHz, well above human hearing). Higher hi-res audio sampling rates of 96 kHz or 192 kHz capture additional headroom above human hearing for processing-and-format flexibility.