Photograph of an electric meter too close to a bed and sleeping area - high EMF will be measured if quite close to electrical meters Definitions of Hertz, Kilohertz, Megahertz, Gigahertz, Terahertz - frequency measures

  • DEFINITIONS of HERTZ, KHz MHz GHz THz - CONTENTS:What are the definitions of common frequency measurements: Hertz, Kilohertz, Megahertz, Gigahertz, & Terahertz?Definition of kHz, MHz, GHz, THz. What kinds of radio frequency waves are there, what are EMF, RF, hertz, megahertz, MF, VHF, UHF, MHz, GHz, THz? Links to EMF measurement explanations, procedures, worksheets, instruments & advice
  • POST a QUESTION or READ FAQs about definitions of frequency measurements: hertz, kilohertz, megahertz, gigahertz, terahertz and cycle counts

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This article defines and compares frequency measurements expressed in Hertz, Kilohertz kHz, Megahertz MHz, Gigahertz GHz, and Terahertz THz .

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Table of Definitions of Kilohertz, Megahertz, Gigahertz, Terahertz

Relation of wavelength to frequency & speed: notice that the shorter the wavelength the higher the frequency. That's why in our table above as the wavelengths get smaller (notice those negative exponents?) the electromagnetic frequency numbers get larger. More technically, wavelength is inversely proportional to wave frequency.

Do not confuse wavelength and frequency of an electromagnetic wave with its speed. All electromagnetic waves move at or close to the speed of light (and do move at the speed of light if measured in a vacuum). The speed of an electromagnetic wave, expressed in meters per second is equal to wavelength (in meters) x frequency (in oscillations per second or Hertz, abbreviated as Hz).

  • Hertz - Hz is defined as the number of cycles per second of any oscillating or repeating phenomenon, but usually used to define electrical signals, or electrical field frequencies such as those of electromagnetic fields, radio signals, or computer processing clock cycles.

    The term Hertz as used in frequency measurement was named for German physicist Heinrich Hertz (1857-1894), who studied electromagnetism, clarified Maxwell's electromagnetic theory of light, and demonstrated the existence of electromagnetic waves. The term Hertz was established by the International Electrotechnical Commission in 1930.
  • Kilohertz - kHz is defined as thousands of cycles per second.
  • Megahertz - MHz is defined as millions of cycles per second - 1000 x more than kilo. See our table below.
  • Gigahertz - GHz is defined as billions of cycles per second - 1000 x more than mega, or 1,000,000,000 cycles per second - Microwave towers, UHF and EHF transmission - operate in the 1GHz to 100GHz range.
  • Terahertz - THz is defined as trillions of cycles per second- Wavelengths at frequencies still higher than EHF - GHz are referred to as Terahertz radiation, but are more familiarly understood as infrared light. Still higher frequencies become light visible to the human eye. One THz is a very high frequency unit of electromagnetic (EM) wave frequency equal to one trillion hertz (10-to-the-12th power Hz)

Our table (below) provides definitions of various frequencies or oscillation rates expressed in kilohertz, megahertz, gigahertz, or terahertz.

Frequency Definitions Frequency in words Frequency in Exponent Form
Definition of Hertz Hz One Hertz - one cycle per second 10-1
Definition of Decahertz daHz Tens of cycles per second 101
Definition of Hectohertz hHz Hundreds of cycles per second


Not in common use

Definition of Kilohertz KHz
One kilohertz - one thousand cycles per second = 1,000 103
Definition of Megahertz MHz
One megahertz - one million cycles per second = 1,000,000 106
Definition of Gigahertz GHz
One gigahertz - one billion cycles per second = 1,000,000,000 109 to 1012 (range)
Definition of Terahertz THz
One terahertz - one trillion of cycles per second = 1,000,000,000,000 1012 to 1015 (range)

The additional Hertz incredibly-high frequencies listed below are not likely to be found in use describing electromagnetic radiation such as those discussed in these articles - these are not in common use, but may be used to describe quantum-mechanical wave functions.

Definition of Petahertz PHz
One petahertz - one followed by 15 zeros, or more formally, One One Petahertz PHZ = 1 x 1015
[cycles per second if we are discussing frequency]
Definition of Exahertz EHz One exahertz - one followed by 18 zeros, or
One EHZ = 1 x 1018


Definition of Zetahertz ZHz One zetahertz -one followed by 21 zeros, or
One ZHz = 1 x 1021
Definition of Yotahertz YHz
One yotahertz - one followed by 24 zeros, or
One YHz = 1 x 1024

Separately at Table of EMR Frequencies we provide a separate listing of the frequency in Hertz of various sources of electromagnetic radiation, ranging from ULF - ultra low frequency sources - through UHF - ultra high frequency electromagnetic radiation sources. Because the possible effects of electromagnetic fields on humans, other animals, and even materials varies significantly by frequency (and wavelength, distance, and other factors).


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DEFINITIONS of HERTZ, KHz MHz GHz THz at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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Frequently Asked Questions (FAQs) about the definitions of Hertz & various frequency measurements

Question: how many zeros in a PetaHertz?

I read in [the article above]

“One petahertz = ten followed by 15 zeros”

I Believe it should be :

One petahertz = one followed by 15 zeros

The same mistake is repeated for the definitions of : Exahertz Zetahertz Yotahertz. - Y. [Annon]


Thank you for the question on clarifying how to write the value of various high-frequency measurements such as Petahertz, Exahertz, etc.

The correct formula for one PHz is 1 x 10 to the 15th power

Since 1 x anything is identical to that "anything",

10 to the 1th is 10

10 to the 2d power is 10 x 10 = 100 (1 followed by two zeroes) making you correct

1 x 10 to the 15th is exactly equal to 10 to the 15th which you could write as


or 1 followed by fifteen zeroes - you are quite correct and we have amended our article text to be more accurate.

Thank you. Daniel Friedman

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