Frequency Converter

1 kHz is 1,000 Hz, and the period is 1 ÷ frequency

Frequency counts how many times the same thing repeats in one second, and its unit is the hertz (Hz). 1 Hz means once per second, which is the same as s⁻¹. Kilo (k), mega (M), giga (G) and tera (T) are decimal prefixes that each step up by a factor of 1,000, so 2.4 GHz is 2,400 MHz, 2,400,000 kHz and 2,400,000,000 Hz. The time one repetition takes is the period, T = 1 ÷ f, so the period at 60 Hz is about 16.67 ms. For radio waves and light, the wavelength is the speed of light divided by the frequency, λ = c ÷ f, which makes a 2.4 GHz signal about 12.49 cm long.

The converter above fills nine fields at once: hertz through terahertz, plus repetitions per minute (rpm), period, vacuum wavelength and angular frequency. Type into any field and the other eight follow. The oscilloscope drawing shows how much of the screen one cycle takes, and the tuning dial and the four readouts below it tell you whether that frequency falls in sound, radio or light.

When you might need it

• Checking mains frequency: North American grids run at 60 Hz and the UK uses 50 Hz. If a nameplate on a gadget you bought abroad says only "50 Hz", check it against your outlet, because anything with a motor in it turns at a speed that depends on the supply frequency.
• Looking for a "frequency converter" device: the same name is also used for equipment that changes the mains itself between 50 Hz and 60 Hz. This page does not change any power supply. It is a calculator that reads one frequency in other units, as a period and as a wavelength, which helps you judge how far a device's speed and timing would shift before you pick hardware.
• Reading audio specs: CDs use 44.1 kHz and most video and broadcast work uses 48 kHz. These numbers say how many times per second the sound is sampled, not how high it sounds.
• Tuning in to radio and wireless gear: turning a frequency into a wavelength shows how long the wave is in space. GPS L1 at 1,575.42 MHz has a wavelength of about 19.03 cm.
• Working with clocks and timers: one cycle of a 16 MHz clock lasts 62.5 ns, and a timer that fires every 1 ms runs at 1 kHz.
• Doing physics homework or rotation problems: 3,000 rpm is 50 turns per second, so 50 Hz, and the angular frequency ω = 2π × f comes to about 314.16 rad/s.

How to use it

1. Type the value you know into the matching field. Thousands commas such as 1,234.5 are fine, and very large or small numbers can be entered as 2.4e9 or 2.4×10^9.
2. The field you typed in becomes the reference (dark outline) and the other eight update. A field holding a rounded value gets a "≈" at the end of its name.
3. The period and wavelength fields pick a readable unit (ms, µs, km, cm and so on) on their own. If you choose a unit yourself it stays until you press Reset or Example, and a number typed into that field is read in the unit you chose.
4. Under "Significant digits" choose 4, 6 or 10. Values of 10¹⁵ or more, or below 0.000001, appear as powers of ten such as 2.4 × 10¹⁵.
5. The oscilloscope picks a time per division in 1-2-5 steps so that roughly two to six cycles fit across ten divisions, and it marks the period T on the first shaded cycle.
6. Drag the tuning dial, or focus it and use ← → (1-2-5 steps) and PageUp PageDown (10×). The four readouts below show that frequency as sound, radio, light and rotation. Clicking a value under "Common values" puts it in the fields above.

How it is calculated

Every field is first converted to hertz, and each other field is then computed from that value. Numbers are kept as exact fractions and rounded once at the end. The speed of light c has been an exact defined value in the International System of Units (SI) since 1983, and the Planck constant h and the elementary charge e since 2019.

Angular frequency involves π, so its field is always a rounded value (≈). The SI keeps the hertz for frequency and rad/s for angular frequency, and the two differ by a factor of 2π, so they should not be mixed up.

Period and wavelength of common frequencies

The table below is rounded to six significant digits. Wavelengths are for a vacuum, so they apply to radio and light. The wavelength of sound is covered separately in the section on sound and pitch.

Radio band names: VLF to EHF

Table 1 of ITU-R Recommendation V.431-8 splits 300 Hz to 3,000 THz into tenfold steps and numbers them from 3 to 15. Band N covers frequencies above 0.3 × 10ᴺ Hz and up to 3 × 10ᴺ Hz. The lower end is excluded and the upper end is included, so 300 MHz belongs to VHF (band 8), not UHF. Only band 3 (ULF) and bands 4 to 11 (VLF to EHF) have letter symbols; from band 12 up there are none. The wavelengths in the metric names assume the speed of light is 3 × 10⁸ m/s.

Light can be read as a frequency in the same way. The International Commission on Illumination (CIE) holds that the limits of visible radiation cannot be fixed sharply, and puts the lower limit at roughly 360 to 400 nm and the upper limit at roughly 760 to 830 nm. On the longer side, 780 nm to 1 mm is infrared, and on the shorter side, 100 to 400 nm is ultraviolet. That is why infrared begins at a 1 mm wavelength, about 300 GHz, right where the EHF band ends. The SI defines the candela through light of 540 × 10¹² Hz (540 THz), which has a wavelength of about 555 nm and a photon energy of about 2.23 eV.

50 Hz, 60 Hz and motor speed

The US Energy Information Administration notes that electric systems in North America are designed and operated to maintain an alternating current frequency of 60 cycles per second (hertz). In the UK, regulation 27 of the Electricity Safety, Quality and Continuity Regulations 2002 sets supply at 230 V and 50 Hz. Korea's standard frequency is 60 Hz with a tolerance of 0.2 Hz either way (Electricity Business Act Enforcement Rule, Annex 3), and Japan is split for historical reasons, with 50 Hz in the east and 60 Hz in the west.

The synchronous speed of an AC motor is "frequency × 120 ÷ number of poles" (ABB Motor Guide). The same motor therefore turns 1.2 times faster on a 60 Hz supply than on a 50 Hz one. Induction motors, which are the most common kind, run slightly slower than this once they are under load.

Whether a 50 Hz-only appliance can safely be plugged into a 60 Hz supply cannot be decided by this calculation. Check the rated frequency on its nameplate and the manufacturer's guidance first.

Sound and pitch: 440 Hz and 432 Hz

People can hear sound from roughly 20 Hz to 20 kHz. Below that range it is called infrasound, and above it, ultrasound. The international standard ISO 16 sets the tuning reference, the note A4, at 440 Hz. In twelve-tone equal temperament an octave doubles the frequency and each semitone multiplies it by the twelfth root of 2 (about 1.0595), so the "As sound" readout names the nearest note relative to 440 Hz and shows how many cents (hundredths of a semitone) you are off from it.

"432 Hz music" means tuning A4 to 432 Hz. Computing 1,200 × log₂(432 ÷ 440) gives about −31.77 cents, so it sits roughly a third of a semitone below 440 Hz tuning.

The wavelength of sound has to be worked out with the speed of sound, not the speed of light. In dry air at 20 °C sound travels about 343 m per second, so a 440 Hz tone has a wavelength of about 78.0 cm, 20 Hz about 17.15 m and 20 kHz about 1.715 cm. A sampling rate of 44.1 kHz means the sound is recorded 44,100 times per second, and by the sampling theorem such a file can hold sound up to half that rate, 22.05 kHz.

Common mistakes

• mHz versus MHz: a lowercase m means milli (10⁻³) and an uppercase M means mega (10⁶), a difference of a factor of a billion. Kilo is a lowercase k, so write kHz, not KHz.
• Treating 1 kHz as 1,024 Hz: SI prefixes mean powers of ten only. The SI Brochure also states that 1 kilobit is 1,000 bits, not 1,024.
• Writing angular frequency in Hz: ω = 2πf is written in rad/s. Writing 314.16 rad/s as "314.16 Hz" would overstate the frequency by a factor of 6.28.
• Confusing GHz with GB or Gbps: GHz is repetitions per second, GB is storage capacity and Gbps is data sent per second. The numbers may match, but the units are not interchangeable.
• Reading a sampling rate as a pitch: a 48 kHz file does not play a 48 kHz tone.
• Hz versus Bq: both are s⁻¹, but the SI reserves the hertz for periodic phenomena and the becquerel for random processes such as radioactive decay.
• Using the vacuum wavelength inside a cable or water: in a material that slows the wave, the same frequency has a shorter wavelength. Divide the speed in that material by the frequency instead.

Limitations

• The wavelength field is for a vacuum. Radio in air is nearly the same, but in cable, glass or water the wavelength is shorter.
• The wavelength in the "As sound" readout uses 343 m/s for dry air at 20 °C. If the temperature changes, so do the speed of sound and the wavelength.
• Note names use twelve-tone equal temperament with A4 = 440 Hz. Instruments tuned to another reference pitch or to just intonation give different cents values.
• Motor speed is the theoretical synchronous speed. A real induction motor turns somewhat slower under load.
• The ITU bands and the CIE divisions of light are conventions, and the limits of visible light in particular differ from person to person.
• Entries from 1 µHz to 10¹⁸ Hz are accepted, with up to 10 significant digits displayed. Angular frequency is computed with π to 74 decimal places.

Basis: the units and constants are defined values in the 9th edition of the BIPM SI Brochure and do not change from year to year. The Korean figure comes from the current text on the National Law Information Center (Annex 3 of the Electricity Business Act Enforcement Rule, amended 2025-10-01), and the other sources were checked against the originals on 21 October 2026.

Sources

• 01BIPM — The International System of Units (SI Brochure), 9th editionTable 4 hertz (Hz = s⁻¹, periodic phenomena only), angular frequency in rad/s and the 2π difference, defining constants c, h, e, SI prefixes are powers of ten, candela 540 × 10¹² Hz
• 02ITU-R Recommendation V.431-8 — Nomenclature of the frequency and wavelength bands used in telecommunicationsBands 4 to 12, symbols VLF to EHF, metric names
• 03Korea National Law Information Center — Enforcement Rule of the Electricity Business Act, art. 18 and Annex 3 (in Korean)Standard frequency 60 Hz, tolerance within 0.2 Hz either way
• 04UK — Electricity Safety, Quality and Continuity Regulations 2002, regulation 27Low-voltage supply 230 V, 50 Hz
• 05U.S. EIA — Hourly Electric Grid Monitor, AboutNorth American electric systems maintain an AC frequency of 60 cycles per second (hertz)
• 06Agency for Natural Resources and Energy (Japan) — Document 3-1 (2022), in JapaneseEastern Japan 50 Hz, western Japan 60 Hz
• 07CIE e-ILV 17-21-003 visible radiation · 17-21-004 infrared · 17-21-008 ultravioletVisible lower limit 360–400 nm, upper limit 760–830 nm, infrared 780 nm–1 mm, ultraviolet 100–400 nm
• 08Britannica — SoundHuman hearing range 20 Hz to 20 kHz
• 09HyperPhysics — Speed of Sound in Air343 m/s in dry air at 20 °C
• 10ISO 16:1975 — Acoustics: Standard tuning frequencyA at 440 Hz
• 11ABB — Motor Guide, 4th editionSynchronous speed (r/min) = frequency × 120 ÷ number of poles
• 12IEC 60908:1999 — Audio recording, Compact disc digital audio systemSampling frequency 44.1 kHz
• 13AES5 — Preferred sampling frequencies for applications employing PCM48 kHz preferred for production, processing and interchange
• 14IS-GPS-200N — Navstar GPS Space Segment/Navigation User InterfacesL1 carrier 1575.42 MHz
• 15ITU-R — Radio Regulations No. 5.150 (ISM)2,400–2,500 MHz, center frequency 2,450 MHz

Frequently asked questions

Related tools