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
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 - GHzis 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 - THzis 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 in words
Frequency in Exponent Form
Definition of Hertz Hz
One Hertz - one cycle per second
Definition of Decahertz daHz
Tens of cycles per second
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
Definition of Megahertz MHz
One megahertz - one million cycles per second = 1,000,000
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).
FAQs below discusses field reports of problems & solutions for this topic
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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Questions & answers or comments about various hertz definitions. .
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"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).
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
"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
"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
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