View source for DBm

{{short description|Power level referenced to one milliwatt}}
{{other uses|DBM (disambiguation)}}
{{lowercase|title=dBm}}
[[File:Relationship between dBu and dBm.svg|thumb|A schematic showing the relationship between [[dBu]] (the [[voltage source]]) and dBm (the power dissipated as [[heat]] by the 600 Ω [[resistor]])]]
'''dBm''' or '''dB<sub>mW</sub>''' (decibel-milliwatts) is a unit of power [[level (logarithmic quantity)|level]] expressed using a [[Logarithmic scale|logarithmic]] [[decibel]] (dB) scale respective to one [[milliwatt]] (mW). It is commonly used by radio, microwave and fiber-optical communication technicians & engineers to measure the [[power (physics)|power]] of system transmissions on a [[log scale]], which can express both very large and very small values in a short form. [[dBW]] is a similar unit measured relative to one watt (1000&nbsp;mW) rather than a milliwatt.

The decibel ('''dB''') is a [[dimensionless unit]], used for quantifying the ratio between two values, such as [[signal-to-noise ratio]]. The dBm is also dimensionless,<ref>{{cite book |last=Green |first=Lynne D. |title=Fiber Optic Communications |publisher=CRC Press |date=2019 |page=181 |isbn=9781000694512 |url=https://books.google.com/books?id=_zf3DwAAQBAJ&pg=PA181}}</ref><ref>{{cite book |last=Kosatsky |first=Tom |title=Radiofrequency Toolkit for Environmental Health Practitioners |publisher=British Columbia Centre for Disease Control |date=2013 |page=8 |url=http://www.bccdc.ca/resource-gallery/Documents/Educational%20Materials/EH/Radiofrequency-Toolkit.pdf#page=14 |archive-url=https://ghostarchive.org/archive/20221009/http://www.bccdc.ca/resource-gallery/Documents/Educational%20Materials/EH/Radiofrequency-Toolkit.pdf#page=14 |archive-date=2022-10-09 |url-status=live}}</ref> but since it compares to a fixed reference value, the dBm quantity is an absolute one.

The dBm is not a part of the [[International System of Units]] (SI) and therefore is discouraged from use in documents or systems that adhere to SI units. (The corresponding SI unit is the watt.) However, the unit [[decibel]] (dB) for relative quantities, without any suffix, is [[International System of Units#Non-SI units accepted for use with SI|a non-SI unit that is accepted for use alongside SI units]]. The level of a power ''P'' of ten decibels relative to one milliwatt may be written ''L''<sub>''P''/(1&nbsp;mW)</sub> = 10&nbsp;dB to comply with the SI.<ref>{{citation| url=http://physics.nist.gov/cuu/pdf/sp811.pdf |last1=Thompson |first1=A. |last2=Taylor |first2=N. |year=2008 |title=Guide for the Use of the International System of Units (SI), NIST Special Publication SP811 |archive-url=https://web.archive.org/web/20160603203340/http://physics.nist.gov/cuu/pdf/sp811.pdf |archive-date=2016-06-03 |at=§8.7 }}</ref>

In audio and telephony, dBm is typically referenced relative to the 600-ohm [[Electrical impedance|impedance]]<ref>{{cite book |last=Bigelow |first=Stephen |title=Understanding Telephone Electronics |year=2001 |publisher=Newnes |isbn=978-0750671750 |pages=[https://archive.org/details/isbn_9780750671750/page/16 16] |url-access=registration |url=https://archive.org/details/isbn_9780750671750/page/16}}</ref> commonly used in telephone voice networks, while in radio-frequency work dBm is typically referenced relative to a 50-ohm impedance.<ref>{{cite book |last=Carr |first=Joseph |title=RF Components and Circuits |url=https://archive.org/details/rfcomponentscirc00carr |url-access=limited |year=2002 |publisher=Newnes |isbn=978-0750648448 |pages=[https://archive.org/details/rfcomponentscirc00carr/page/n62 45]–46 }}</ref>

== Unit conversions ==
A power level of 0&nbsp;dBm corresponds to a power of 1 milliwatt. An increase in level of 10&nbsp;dB is equivalent to a ten-fold increase in power. Therefore, a 20&nbsp;dB increase in level is equivalent to a 100-fold increase in power. A 3&nbsp;dB increase in level is approximately equivalent to doubling the power, which means that a level of 3&nbsp;dBm corresponds roughly to a power of 2&nbsp;mW. Similarly, for each 3&nbsp;dB decrease in level, the power is reduced by about one half, making −3&nbsp;dBm correspond to a power of about 0.5&nbsp;mW.

To express an arbitrary power {{mvar|P}} in mW as {{mvar|x}} in dBm, the following expression may be used:<ref>{{cite book |last=Sobot |first=Robert |title=Wireless Communication Electronics: Introduction to RF Circuits and Design |publisher=Springer |date=2012 |page=252 |isbn=9783030486303 |url=https://books.google.com/books?id=pdX-DwAAQBAJ&pg=PA252}}</ref>
<math display="block">\begin{align}
 x &= 10 \log_{10} \frac{P}{1~\text{mW}}
\end{align}</math>
Conversely, to express an arbitrary power level {{mvar|x}} in dBm, as {{mvar|P}} in mW:
<math display="block">\begin{align}
 P &= 1~\text{mW} \cdot 10^{{x}/{10}}
\end{align}</math>

== Table of examples ==
Below is a table summarizing useful cases:

{{Main|Orders of magnitude (power)}}
{| class="wikitable"
! Power&nbsp;level !! Power !! Notes
|-
|526 dBm || {{val|3.6|e=49|u=W}} || [[First observation of gravitational waves|Black hole collision]], the power radiated in gravitational waves following the collision [[First observation of gravitational waves|GW150914]], estimated at 50 times the power output of all the stars in the observable universe<ref>{{cite web |title=Observation of gravitational waves from a binary black hole merger |url=https://www.ligo.caltech.edu/system/media_files/binaries/301/original/detection-science-summary.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.ligo.caltech.edu/system/media_files/binaries/301/original/detection-science-summary.pdf |archive-date=2022-10-09 |url-status=live|website=LSC (Ligo Scientific Collaboration) |publisher=Caltech |date=2015 |access-date=10 April 2021}}</ref><ref>{{cite web |title=Found! Gravitational Waves, or a Wrinkle in Spacetime|url=https://www.nationalgeographic.com/science/article/160211-gravitational-waves-found-spacetime-science|archive-url=https://web.archive.org/web/20210224182310/https://www.nationalgeographic.com/science/article/160211-gravitational-waves-found-spacetime-science|url-status=dead|archive-date=February 24, 2021|website=National Geographic|date=2016-02-11|access-date=2021-04-10}}</ref>
|-
|420 dBm || {{val|1|e=39|u=W}} || [[Cygnus A]], one of the most powerful radio sources in the sky
|-
|296 dBm || {{val|3.846|e=26|u=W}} || Total power output of the Sun<ref>{{cite web |title=Ask Us: Sun |url=https://helios.gsfc.nasa.gov/qa_sun.html
|archive-url=https://web.archive.org/web/20000816180724/http://helios.gsfc.nasa.gov/qa_sun.html
|url-status=dead
|archive-date=2000-08-16
|website=Cosmicopia |publisher=NASA |date=2012 |access-date=13 July 2017}}</ref>
|-
|-
|120 dBm || 1&nbsp;GW || Experimental high-power microwave (HPM) generation system, 1&nbsp;GW at 2.32&nbsp;GHz for 38&nbsp;ns<ref>{{cite journal |last1=Li |first1=Wei |last2=Li |first2=Zhi-qiang |last3=Sun |first3=Xiao-liang |last4=Zhang |first4=Jun |date=2015-11-01 |title=A reliable, compact, and repetitive-rate high power microwave generation system |url=https://aip.scitation.org/doi/full/10.1063/1.4935500 |journal=Review of Scientific Instruments |volume=86 |issue=11 |pages=114704 |doi=10.1063/1.4935500 |pmid=26628156 |bibcode=2015RScI...86k4704L |issn=0034-6748 |url-access=subscription}}</ref>
|-
| 105 dBm || 32&nbsp;MW || [[Eglin AFB Site C-6|AN/FPS-85 Phased Array Space Surveillance Radar]], claimed by the US Space Force as the most powerful radar in the world<ref name="AirForceFactSheet">
{{cite web
 | title = AN/FPS-85
 | work = US Air Force Fact Sheet
 | publisher = United States Dept. of Defense
 | url = http://www.radomes.org/museum/equip/fps-85.html
 | access-date = May 19, 2017
}}</ref>
|-
| 95.5 dBm || 3600&nbsp;kW || [[High-frequency Active Auroral Research Program]] maximum power output, the most powerful shortwave station in 2012
|-
| 80 dBm || 100&nbsp;kW || Typical [[Effective radiated power|transmission power]] of [[FM radio]] station with {{convert|adj=on|50|km|mi}} range
|-
| 62 dBm || 1.588&nbsp;kW ||1.5&nbsp;kW is the maximum legal power output of a US [[ham radio]] station.<ref>{{cite web |url=http://www.arrl.org/part-97-amateur-radio|title=Part 97 - Amateur Radio |publisher=ARRL |access-date=2012-09-21 |archive-url=https://web.archive.org/web/20121009015812/http://www.arrl.org/part-97-amateur-radio |archive-date=2012-10-09 |url-status=live}}</ref> 
|-
| 60 dBm || 1&nbsp;kW || Typical combined radiated RF power of [[microwave oven]] elements
|- 
| 55 dBm || ~300 W || Typical single-channel RF output power of a [[Ku band|K<sub>u</sub> band]] [[geostationary satellite]]
|- 
| 50 dBm || 100 W || Typical total [[Black-body radiation#Human-body emission|thermal radiation emitted by a human body]], peak at 31.5&nbsp;THz (9.5&nbsp;μm){{br}} Typical maximum output RF power from a [[ham radio]] [[High frequency|HF]] transceiver without power amplifier
|- 
| 40 dBm || 10 W || Typical [[power-line communication]] (PLC) transmission power
|-
| 37 dBm || 5 W || Typical maximal output RF power from a handheld ham radio VHF/UHF transceiver
|-
| 36 dBm || 4 W || Typical maximal output power for a [[citizens band radio]] station (27&nbsp;MHz) in many countries
|-
| 33 dBm || 2 W || Maximal output from a [[UMTS]]/[[3G]] mobile phone (power class 1 mobiles){{br}} Maximal output from a GSM850/900 mobile phone
|-
| 30 dBm || 1 W || DCS or GSM 1800/1900&nbsp;MHz mobile phone.{{br}} [[EIRP]] IEEE 802.11a (20&nbsp;MHz-wide channels) in either 5&nbsp;GHz subband 2 (5470–5725&nbsp;MHz) provided that transmitters are also IEEE 802.11h-compliant, ''or'' [[U-NII]]-3 (5725–5825&nbsp;MHz). The former is EU only, the latter is US only. Also, maximal power allowed by the FCC for American amateur radio licensees to fly [[radio-controlled aircraft]] or operate RC models of any other type on the amateur radio bands in the US.<ref>[http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&SID=336ab7469b61ecbfa15086dbf1bf2c59&rgn=div5&view=text&node=47:5.0.1.1.6&idno=47#se47.5.97_1215] {{Webarchive|url=https://web.archive.org/web/20161222021621/http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&rgn=div5&view=text&node=47:5.0.1.1.6&idno=47#se47.5.97_1215|date=2016-12-22}} FCC Part 97 Amateur Radio Service - Rule 97.215, ''Telecommand of model craft'', section (c).</ref>
|-
| 27 dBm || 500&nbsp;mW || Typical [[cellular phone]] transmission power{{br}} Maximal output from a UMTS/3G mobile phone (power class 2 mobiles)
|-
| 24 dBm || 251&nbsp;mW || Maximal output from a UMTS/3G mobile phone (power class 3 mobiles){{br}} 1880–1900&nbsp;MHz [[DECT]] (250&nbsp;mW per 1728&nbsp;kHz channel).{{br}} [[EIRP]] for wireless LAN IEEE 802.11a (20&nbsp;MHz-wide channels) in either the 5&nbsp;GHz subband 1 (5180–5320&nbsp;MHz) or [[U-NII]]-2 and -W ranges (5250–5350&nbsp;MHz & 5470–5725&nbsp;MHz, respectively). The former is EU only, the latter is US only.
|-
| 23 dBm || 200&nbsp;mW || [[EIRP]] for IEEE 802.11n wireless LAN 40&nbsp;MHz-wide (5&nbsp;mW/MHz) channels in 5&nbsp;GHz subband 4 (5735–5835&nbsp;MHz, US only) or 5&nbsp;GHz subband 2 (5470–5725&nbsp;MHz, EU only). Also applies to 20&nbsp;MHz-wide (10&nbsp;mW/MHz) IEEE 802.11a wireless LAN in 5&nbsp;GHz subband 1 (5180–5320&nbsp;MHz) ''if'' also IEEE 802.11h-compliant (otherwise only 3&nbsp;mW/MHz → 60&nbsp;mW when unable to dynamically adjust transmission power, and only 1.5&nbsp;mW/MHz → 30&nbsp;mW when a transmitter also cannot [[Dynamic Frequency Selection|dynamically select frequency]])
|-
| 21 dBm || 125&nbsp;mW || Maximal output from a UMTS/3G mobile phone (power class 4 mobiles)
|-
| 20 dBm || 100&nbsp;mW || [[EIRP]] for IEEE 802.11b/g wireless LAN 20&nbsp;MHz-wide channels in the 2.4&nbsp;GHz [[Wi-Fi]]/[[ISM band]] (5&nbsp;mW/MHz).{{br}} [[Bluetooth]] Class 1 radio.{{br}} Maximal output power from unlicensed [[Amplitude modulation|AM]] [[transmitter]] per US [[Federal Communications Commission|FCC]] rules 15.219<ref>[http://www.hallikainen.org/FCC/FccRules/CiteFind/015219.htm FCC Web Documents citing 15.219] {{webarchive |url=https://web.archive.org/web/20111106230158/http://www.hallikainen.org/FCC/FccRules/CiteFind/015219.htm |date=2011-11-06 }}</ref>
|-
| 15 dBm || 32&nbsp;mW || Typical [[wireless LAN]] transmission power in laptops
|-
| 7 dBm || 5.0&nbsp;mW || Common power level required to test the [[automatic gain control]] circuitry in an AM receiver
|-
| 4 dBm || 2.5&nbsp;mW || Bluetooth Class 2 radio, 10&nbsp;m-range
|-
| 0 dBm || 1.0&nbsp;mW || Bluetooth standard (Class 3) radio, 1&nbsp;m-range
|-
| −10 dBm || 100&nbsp;μW || Maximal received signal power of [[wireless network]] (802.11 variants)
|-
| −13 dBm || 50&nbsp;μW || Dial tone for the [[precise tone plan]] found on [[public switched telephone network]]s in [[North America]]
|-
| −20 dBm || 10&nbsp;μW ||
|-
| −30 dBm || 1.0&nbsp;μW ||  
|-
| −40 dBm || 100&nbsp;[[Watt#Multiples|nW]] ||
|-
| −50 dBm || 10&nbsp;nW ||
|-
| −60 dBm || 1.0&nbsp;nW || The [[Earth]] receives one nanowatt per square metre from a [[star]] of  [[apparent magnitude]] +3.5<ref>{{cite web |title=Radiant Flux of a Magnitude +3.5 Star |url=http://webhome.cs.uvic.ca/~pearson/files/radiant_flux.html |archive-url=https://archive.today/20120630221250/http://webhome.cs.uvic.ca/~pearson/files/radiant_flux.html |archive-date=2012-06-30 |url-status=dead |access-date=2009-07-22 }}</ref>
|-
| −70 dBm || 100 [[Watt#Multiples|pW]] || 
|-
| −73 dBm || 50.12 pW || "S9" signal strength, a strong signal, on the [[S meter]] of a typical [[Amateur radio|ham]] or [[shortwave radio receiver]]
|-
| −80 dBm || 10 pW || 
|-
| −100 dBm || 0.1 pW || Minimal received signal power of [[wireless network]] (802.11 variants)
|-
| −111 dBm || 8&nbsp;[[Watt#Multiples|fW]] || [[Johnson–Nyquist noise|Thermal noise floor]] for commercial [[GPS]] single-channel signal bandwidth (2&nbsp;MHz)
|-
| −127.5 dBm || 0.178 fW || Typical received signal power from a [[GPS satellite]]
|-
| −174 dBm || 4&nbsp;[[Watt#Multiples|zW]]|| Thermal noise floor for 1&nbsp;Hz bandwidth at room temperature (20&nbsp;°C)
|-
| −192.5 dBm || 56&nbsp;[[Watt#Multiples|yW]] || Thermal noise floor for 1&nbsp;Hz bandwidth in outer space ({{val|4|ul=K}})
|-
| −∞ dBm || 0 W || Zero power (value is [[negative infinity]])
|}

== Standards ==
The signal intensity (power per unit area) can be converted to received signal power by multiplying by the square of the wavelength and dividing by 4{{pi}} (see [[Free-space path loss]]).

In [[United States Department of Defense]] practice, [[Weighting filter|unweighted]] measurement is normally understood, applicable to a certain [[Bandwidth (signal processing)|bandwidth]], which must be stated or implied.{{citation needed|date=July 2025}}

In European practice, [[psophometric weighting]] may be, as indicated by context, equivalent to [[dBm0p]], which is preferred.{{citation needed|date=July 2025}}

In audio, 0&nbsp;dBm often corresponds to approximately 0.775 volts, since 0.775&nbsp;V dissipates 1&nbsp;mW in a 600&nbsp;Ω load.<ref name=srh/> The corresponding voltage level is 0 [[Decibel#Voltage|dBu]], without the 600&nbsp;Ω restriction. Conversely, for RF situations with a 50&nbsp;Ω load, 0&nbsp;dBm corresponds to approximately 0.224 volts, since 0.224&nbsp;V dissipates 1&nbsp;mW in a 50&nbsp;Ω load.{{citation needed|date=July 2025}}

In general the relationship between the level of a power {{mvar|P}} in dBm and the [[root mean square|{{abbr|RMS|root mean square}}]] voltage {{mvar|V}} in volts across a load of resistance {{mvar|R}} (typically used to terminate a transmission line with impedance {{mvar|Z}}) is:
<math display="block">\begin{align}
 V &= \sqrt{R \frac{10^{P/10}}{1000}}\,.
\end{align}</math>

Expression in dBm is typically used for optical and electrical power measurements, not for other types of power (such as thermal). A [[Orders of magnitude (power)|listing by power levels in watts]] is available that includes a variety of examples not necessarily related to electrical or optical power.

The dBm was first proposed as an industry standard<ref name=srh>{{cite book |last=Davis |first=Gary |title=The Sound Reinforcement Handbook |year=1988 |publisher=Yamaha |isbn=0881889008 |pages=22 }}</ref> in 1940.<ref>{{cite journal |last=Chinn |first=H. A. |first2=D. K. |last2=Gannett |first3=R. M. |last3=Moris |title=A New Standard Volume Indicator and Reference Level |journal=Proceedings of the Institute of Radio Engineers |date=January 1940 |volume=28 |issue=1 |pages=1–17 |doi=10.1109/JRPROC.1940.228815 |s2cid=15458694 |url=http://www.aes.org/aeshc/pdf/chinn_a-new-svi.pdf |access-date=2012-08-04 |archive-url=https://web.archive.org/web/20120213001201/http://www.aes.org/aeshc/pdf/chinn_a-new-svi.pdf |archive-date=2012-02-13 |url-status=live }}</ref>

== See also ==
* [[Decibel watt]]
* [[dBm0]]

== References ==
{{FS1037C MS188}}
{{reflist}}

== External links ==
* [http://www.sengpielaudio.com/calculator-volt.htm The dBm calculator for impedance matching]
* [http://cgi.www.telestrian.co.uk/cgi-bin/www.telestrian.co.uk/dBm.pl Convert dBm to watts]
{{Decibel}}

{{DEFAULTSORT:Dbm}}
[[Category:Units of power]]
[[Category:Radio frequency propagation]]
[[Category:Logarithmic scales of measurement]]