Definitions of Hertz, Kilohertz, Megahertz, Gigahertz, Terahertz - frequency measures

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
EMF RF FIELD & FREQUENCY DEFINITIONS - separate article
Questions & Answers about definitions of frequency measurements: hertz, kilohertz, megahertz, gigahertz, terahertz and cycle counts
References

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

Table of Definitions of Kilohertz, Megahertz, Gigahertz, Terahertz

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), readers should also see EMF RF FIELD & FREQUENCY DEFINITIONS.

Also see Definitions of Gauss vs Milligauss for details about gauss and milligauss and definitions of these terms. Also see Electric Power Lines, Electromagnetic Fields, Cancer Risk, & "Enviro-Scare" - The Normal Curve Cycle of Public Fear of Environmental Issues which discusses the impact of EMF and other environmental concerns on property values. And see EMF ELECTROMAGNETIC FIELDS & HUMAN EXPOSURE which discusses EMF exposure in the workplace.

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	10² 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]	10¹⁵
Definition of Exahertz EHz	One exahertz - one followed by 18 zeros, or One EHZ = 1 x 10¹⁸	10¹⁸
Definition of Zetahertz ZHz	One zetahertz -one followed by 21 zeros, or One ZHz = 1 x 10²¹	10²¹
Definition of Yotahertz YHz	One yotahertz - one followed by 24 zeros, or One YHz = 1 x 10²⁴	10²⁴

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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]

Reply:

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

1,000,000,000,000,000

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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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

"San Francisco Law Will Make Cellphone Retailers List Radiation Rate", Jesse McKinley, The New York Times, 16 June 2010 p. A14.
Electric Power Lines, Electromagnetic Fields, Cancer Risk, & "Enviro-Scare" - The Normal Curve Cycle of Public Fear About Environmental Issues - online document by DF
A Procedure for Measuring EMF electromagnetic fields online document by DF
"Questions and Answers about Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields", Federal Communications Commission, Office of Engineering and Technology, US FCC, OET Bulleting 56, 4th Edition, August 1999
" Many consumer and industrial products and applications make use of some form of electromagnetic energy. One type of electromagnetic energy that is of increasing importance worldwide is radiofrequency (or "RF") energy, including radio waves and microwaves, which is used for providing telecommunications, broadcast and other services. In the United States the Federal Communications Commission (FCC) authorizes or licenses most RF telecommunications services, facilities, and devices used by the public, industry and state and local governmental organizations. Because of its regulatory responsibilities in this area the FCC often receives inquiries concerning whether there are potential safety hazards due to human exposure to RF energy emitted by FCC-regulated transmitters. Heightened awareness of the expanding use of RF technology has led some people to speculate that "electromagnetic pollution" is causing significant risks to human health from environmental RF electromagnetic fields. This document is designed to provide factual information and to answer some of the most commonly asked questions related to this topic." - original source: U.S. Federal Communications Commission Office of Engineering and Technology, http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet56/oet56e4.pdf
"Magnetic Field Exposure and Cancer: Questions and Answers [ copy on file as /emf/EMF_Fact_Sheet_NCI_NIH.pdf ] - ," National Cancer Institute, U.S. National Institutes of Health, web search September 2010, original source: http://www.cancer.gov/cancertopics/factsheet/Risk/magnetic-fields
makes these five key points about EMF
- Electric and magnetic fields (EMF) are areas of energy that surround any electrical device. EMFs are produced by power lines, electrical wiring, and appliances (see Question 1).
- Electric fields are easily shielded or weakened by walls and other objects, whereas magnetic fields are not. Since magnetic fields are more likely to penetrate the body, they are the component of EMFs that are usually studied in relation to cancer (see Question 1).
- Overall, there is limited evidence that magnetic fields cause childhood leukemia, and there is inadequate evidence that these magnetic fields cause other cancers in children (see Question 2).
- Studies of magnetic field exposure from power lines and electric blankets in adults show little evidence of an association with leukemia, brain tumors, or breast cancer (see Question 3).
- Past studies of occupational magnetic field exposure in adults showed very small increases in leukemia and brain tumors. However, more recent, well-conducted studies have shown inconsistent associations with leukemia, brain tumors, and breast cancer (see Question 4).
EMF RF FIELD & FREQUENCY DEFINITIONS RF and EMF measurement tools need to be properly chosen to measure the particular type and frequency of RF or EMF signal that is of interest. See EMF RF FIELD & FREQUENCY DEFINITIONS for a simple explanation of different types of radio frequency (RF) and electromagnetic frequency (EMF) types and where they are found.
Definitions of Gauss vs Milligauss for details about gauss and milligauss and definitions of these terms.
Electric Power Lines, Electromagnetic Fields, Cancer Risk, & "Enviro-Scare" - The Normal Curve Cycle of Public Fear of Environmental Issues
Electromagnetic Fields in the Workplace sample very good NIOSH document online, links to other NIOSH docs.
Electromagnetic Field Surveys & Hazards full list of our links to services and technical article
Electric Power Lines, Electromagnetic Fields, Cancer Risk, & "Enviro-Scare" - The Normal Curve Cycle of Public Fear About Environmental Issues - online document by DF
A Procedure for Measuring EMF electromagnetic fields online document by DF

References for Electromagnetic Fields and Cancer Risk/Carcinogenicity

Consumer Product Safety Commission, 800-638-CPSC.
US Environmental Protection Agency, Office of Pesticides and Toxic Substances, TSCA Assistance Office (TS-799), 800-424-9065 or 202-554-1404.
"Evaluation of Potential Carcinogenicity of Electromagnetic Fields," EPA Report #EPA/600/6-90/005B October 1990. EPA: 513/569-7562.
"Biological Effects of Power Frequency Electric and Magnetic Fields" background paper, prepared as part of OTA's assessment of "Electric Power Wheeling and Dealing: Technological Considerations for Increasing Competition," prepared for OTA by Indira Nair, M. Granger Morgan, H. Keith Florig, Department of Engineering and Public Policy, Carnegie Mellon University, Pittsburgh, PA 15213
"Biological Effects of Power Line Fields," New York State Powerline Project. Scientific Advisory Board Final Report, July 1, 1987.
"Extremely Low Frequency (ELF) Fields," Environmental Health Criteria 35. World Health Organization, Geneva, 1984.
"Electric and Magnetic Fields at Extremely Low Frequencies: Interactions with Biological Systems. In: Non ionizing Radiation Protection, World Health Organization, Regional Office for Europe, Copenhagen, 1987.
"Electric and Magnetic Fields from 60 Hertz Electric Power: What do we know about possible health risks?," Department of Engineering and Public Policy, Carnegie Mellon University, Pittsburgh, PA 15213 1989.
"Electromagnetic Fields Are Being Scrutinized for Linkage to Cancer," Sandra Blakeslee, New York Times, Medical Science section, April 2, 1991

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