# DBm

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For other uses, see [DBM (disambiguation)](/source/DBM_(disambiguation)).

**dBm** or **dBmW** (decibel-milliwatts) is a unit of power [level](/source/Level_(logarithmic_quantity)) expressed using a [logarithmic](/source/Logarithmic_scale) [decibel](/source/Decibel) (dB) scale respective to one [milliwatt](/source/Milliwatt) (mW). It is commonly used by radio, microwave and fiber-optical communication technicians & engineers to measure the [power](/source/Power_(physics)) of system transmissions on a [log scale](/source/Log_scale), which can express both very large and very small values in a short form. [dBW](/source/DBW) is a similar unit measured relative to one watt (1000 mW) rather than a milliwatt.

The decibel (**dB**) is a [dimensionless unit](/source/Dimensionless_unit), used for quantifying the ratio between two values, such as [signal-to-noise ratio](/source/Signal-to-noise_ratio). The dBm is also dimensionless,[1][2] 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](/source/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](/source/Decibel) (dB) for relative quantities, without any suffix, is [a non-SI unit that is accepted for use alongside SI units](/source/International_System_of_Units#Non-SI_units_accepted_for_use_with_SI). The level of a power *P* of ten decibels relative to one milliwatt may be written *L**P*/(1 mW) = 10 dB to comply with the SI.[3]

In audio and telephony, dBm is typically referenced relative to the 600-ohm [impedance](/source/Electrical_impedance)[4] commonly used in telephone voice networks, while in radio-frequency work dBm is typically referenced relative to a 50-ohm impedance.[5]

## Unit conversions

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

To express an arbitrary power P in mW as x in dBm, the following expression may be used:[6]

\begin{align}
 x &= 10 \log_{10} \frac{P}{1~\text{mW}}
\end{align}

Conversely, to express an arbitrary power level x in dBm, as P in mW:

\begin{align}
 P &= 1~\text{mW} \cdot 10^{{x}/{10}}
\end{align}

## Table of examples

Below is a table summarizing useful cases:

Main article: [Orders of magnitude (power)](/source/Orders_of_magnitude_(power))

Power level Power Notes 526 dBm 3.6×1049 W Black hole collision, the power radiated in gravitational waves following the collision GW150914, estimated at 50 times the power output of all the stars in the observable universe[7][8] 420 dBm 1×1039 W Cygnus A, one of the most powerful radio sources in the sky 296 dBm 3.846×1026 W Total power output of the Sun[9] 120 dBm 1 GW Experimental high-power microwave (HPM) generation system, 1 GW at 2.32 GHz for 38 ns[10] 105 dBm 32 MW AN/FPS-85 Phased Array Space Surveillance Radar, claimed by the US Space Force as the most powerful radar in the world[11] 95.5 dBm 3600 kW High-frequency Active Auroral Research Program maximum power output, the most powerful shortwave station in 2012 80 dBm 100 kW Typical transmission power of FM radio station with 50-kilometre (31-mile) range 62 dBm 1.588 kW 1.5 kW is the maximum legal power output of a US ham radio station.[12] 60 dBm 1 kW Typical combined radiated RF power of microwave oven elements 55 dBm ~300 W Typical single-channel RF output power of a Ku band geostationary satellite 50 dBm 100 W Typical total thermal radiation emitted by a human body, peak at 31.5 THz (9.5 μm) Typical maximum output RF power from a ham radio 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 MHz) in many countries 33 dBm 2 W Maximal output from a UMTS/3G mobile phone (power class 1 mobiles) Maximal output from a GSM850/900 mobile phone 30 dBm 1 W DCS or GSM 1800/1900 MHz mobile phone. EIRP IEEE 802.11a (20 MHz-wide channels) in either 5 GHz subband 2 (5470–5725 MHz) provided that transmitters are also IEEE 802.11h-compliant, or U-NII-3 (5725–5825 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.[13] 27 dBm 500 mW Typical cellular phone transmission power Maximal output from a UMTS/3G mobile phone (power class 2 mobiles) 24 dBm 251 mW Maximal output from a UMTS/3G mobile phone (power class 3 mobiles) 1880–1900 MHz DECT (250 mW per 1728 kHz channel). EIRP for wireless LAN IEEE 802.11a (20 MHz-wide channels) in either the 5 GHz subband 1 (5180–5320 MHz) or U-NII-2 and -W ranges (5250–5350 MHz & 5470–5725 MHz, respectively). The former is EU only, the latter is US only. 23 dBm 200 mW EIRP for IEEE 802.11n wireless LAN 40 MHz-wide (5 mW/MHz) channels in 5 GHz subband 4 (5735–5835 MHz, US only) or 5 GHz subband 2 (5470–5725 MHz, EU only). Also applies to 20 MHz-wide (10 mW/MHz) IEEE 802.11a wireless LAN in 5 GHz subband 1 (5180–5320 MHz) if also IEEE 802.11h-compliant (otherwise only 3 mW/MHz → 60 mW when unable to dynamically adjust transmission power, and only 1.5 mW/MHz → 30 mW when a transmitter also cannot dynamically select frequency) 21 dBm 125 mW Maximal output from a UMTS/3G mobile phone (power class 4 mobiles) 20 dBm 100 mW EIRP for IEEE 802.11b/g wireless LAN 20 MHz-wide channels in the 2.4 GHz Wi-Fi/ISM band (5 mW/MHz). Bluetooth Class 1 radio. Maximal output power from unlicensed AM transmitter per US FCC rules 15.219[14] 15 dBm 32 mW Typical wireless LAN transmission power in laptops 7 dBm 5.0 mW Common power level required to test the automatic gain control circuitry in an AM receiver 4 dBm 2.5 mW Bluetooth Class 2 radio, 10 m-range 0 dBm 1.0 mW Bluetooth standard (Class 3) radio, 1 m-range −10 dBm 100 μW Maximal received signal power of wireless network (802.11 variants) −13 dBm 50 μW Dial tone for the precise tone plan found on public switched telephone networks in North America −20 dBm 10 μW −30 dBm 1.0 μW −40 dBm 100 nW −50 dBm 10 nW −60 dBm 1.0 nW The Earth receives one nanowatt per square metre from a star of apparent magnitude +3.5[15] −70 dBm 100 pW −73 dBm 50.12 pW "S9" signal strength, a strong signal, on the S meter of a typical 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 fW Thermal noise floor for commercial GPS single-channel signal bandwidth (2 MHz) −127.5 dBm 0.178 fW Typical received signal power from a GPS satellite −159 dBm 0.128 aW Power corresponding to a single 1550-nm wavelength photon per second, typical of the dark count of the best photodetectors (superconducting nanowire single-photon detectors, transition-edge sensors). −174 dBm 4 zW Thermal noise floor for 1 Hz bandwidth at room temperature (20 °C) −192.5 dBm 56 yW Thermal noise floor for 1 Hz bandwidth in outer space (4 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 4π (see [Free-space path loss](/source/Free-space_path_loss)).

In [United States Department of Defense](/source/United_States_Department_of_Defense) practice, [unweighted](/source/Weighting_filter) measurement is normally understood, applicable to a certain [bandwidth](/source/Bandwidth_(signal_processing)), which must be stated or implied.[citation needed]

In European practice, [psophometric weighting](/source/Psophometric_weighting) may be, as indicated by context, equivalent to [dBm0p](/source/DBm0p), which is preferred.[citation needed]

In audio, 0 dBm often corresponds to approximately 0.775 volts, since 0.775 V dissipates 1 mW in a 600 Ω load.[16] The corresponding voltage level is 0 [dBu](/source/Decibel#Voltage), without the 600 Ω restriction. Conversely, for RF situations with a 50 Ω load, 0 dBm corresponds to approximately 0.224 volts, since 0.224 V dissipates 1 mW in a 50 Ω load.[citation needed]

In general the relationship between the level of a power P in dBm and the [RMS](/source/Root_mean_square) voltage V in volts across a load of resistance R (typically used to terminate a transmission line with impedance Z) is:

\begin{align}
 V &= \sqrt{R \frac{10^{P/10}}{1000}}\,.
\end{align}

Expression in dBm is typically used for optical and electrical power measurements, not for other types of power (such as thermal). A [listing by power levels in watts](/source/Orders_of_magnitude_(power)) 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[16] in 1940.[17]

## See also

- [Decibel watt](/source/Decibel_watt)
- [dBm0](/source/DBm0)

## References

1. Green, Lynne D. (2019). [*Fiber Optic Communications*](https://books.google.com/books?id=_zf3DwAAQBAJ&pg=PA181). CRC Press. p. 181. ISBN 9781000694512.

1. Kosatsky, Tom (2013). [*Radiofrequency Toolkit for Environmental Health Practitioners*](http://www.bccdc.ca/resource-gallery/Documents/Educational%20Materials/EH/Radiofrequency-Toolkit.pdf#page=14). British Columbia Centre for Disease Control. p. 8. [Archived](https://ghostarchive.org/archive/20221009/http://www.bccdc.ca/resource-gallery/Documents/Educational%20Materials/EH/Radiofrequency-Toolkit.pdf#page=14) 2022-10-09 at the Wayback Machine.

1. Thompson, A. & Taylor, N. (2008), ["Guide for the Use of the International System of Units (SI), NIST Special Publication SP811"](http://physics.nist.gov/cuu/pdf/sp811.pdf), §8.7, [archived](https://web.archive.org/web/20160603203340/http://physics.nist.gov/cuu/pdf/sp811.pdf) 2016-06-03 at the Wayback Machine

1. Bigelow, Stephen (2001). [*Understanding Telephone Electronics*](https://archive.org/details/isbn_9780750671750/page/16). Newnes. pp. [16](https://archive.org/details/isbn_9780750671750/page/16). ISBN 978-0750671750.

1. Carr, Joseph (2002). [*RF Components and Circuits*](https://archive.org/details/rfcomponentscirc00carr). Newnes. pp. [45](https://archive.org/details/rfcomponentscirc00carr/page/n62)–46. ISBN 978-0750648448.

1. Sobot, Robert (2012). [*Wireless Communication Electronics: Introduction to RF Circuits and Design*](https://books.google.com/books?id=pdX-DwAAQBAJ&pg=PA252). Springer. p. 252. ISBN 9783030486303.

1. ["Observation of gravitational waves from a binary black hole merger"](https://www.ligo.caltech.edu/system/media_files/binaries/301/original/detection-science-summary.pdf). *LSC (Ligo Scientific Collaboration)*. Caltech. 2015. [Archived](https://ghostarchive.org/archive/20221009/https://www.ligo.caltech.edu/system/media_files/binaries/301/original/detection-science-summary.pdf) 2022-10-09 at the Wayback Machine. Retrieved 10 April 2021.

1. ["Found! Gravitational Waves, or a Wrinkle in Spacetime"](https://web.archive.org/web/20210224182310/https://www.nationalgeographic.com/science/article/160211-gravitational-waves-found-spacetime-science). *National Geographic*. 2016-02-11. Archived from [the original](https://www.nationalgeographic.com/science/article/160211-gravitational-waves-found-spacetime-science) on February 24, 2021. Retrieved 2021-04-10.

1. ["Ask Us: Sun"](https://web.archive.org/web/20000816180724/http://helios.gsfc.nasa.gov/qa_sun.html). *Cosmicopia*. NASA. 2012. Archived from [the original](https://helios.gsfc.nasa.gov/qa_sun.html) on 2000-08-16. Retrieved 13 July 2017.

1. Li, Wei; Li, Zhi-qiang; Sun, Xiao-liang; Zhang, Jun (2015-11-01). ["A reliable, compact, and repetitive-rate high power microwave generation system"](https://aip.scitation.org/doi/full/10.1063/1.4935500). *Review of Scientific Instruments*. **86** (11): 114704. [Bibcode:2015RScI...86k4704L](https://ui.adsabs.harvard.edu/abs/2015RScI...86k4704L). [doi:10.1063/1.4935500](https://doi.org/10.1063/1.4935500). [ISSN 0034-6748](https://www.worldcat.org/issn/0034-6748). [PMID 26628156](https://pubmed.ncbi.nlm.nih.gov/26628156)

1. ["AN/FPS-85"](http://www.radomes.org/museum/equip/fps-85.html). *US Air Force Fact Sheet*. United States Dept. of Defense. Retrieved May 19, 2017.

1. ["Part 97 - Amateur Radio"](http://www.arrl.org/part-97-amateur-radio). ARRL. [Archived](https://web.archive.org/web/20121009015812/http://www.arrl.org/part-97-amateur-radio) 2012-10-09 at the Wayback Machine. Retrieved 2012-09-21.

1. [\[1\]](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) [Archived](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) 2016-12-22 at the Wayback Machine FCC Part 97 Amateur Radio Service - Rule 97.215, *Telecommand of model craft*, section (c).

1. [FCC Web Documents citing 15.219](http://www.hallikainen.org/FCC/FccRules/CiteFind/015219.htm) [Archived](https://web.archive.org/web/20111106230158/http://www.hallikainen.org/FCC/FccRules/CiteFind/015219.htm) 2011-11-06 at the Wayback Machine

1. ["Radiant Flux of a Magnitude +3.5 Star"](https://archive.today/20120630221250/http://webhome.cs.uvic.ca/~pearson/files/radiant_flux.html). Archived from [the original](http://webhome.cs.uvic.ca/~pearson/files/radiant_flux.html) on 2012-06-30. Retrieved 2009-07-22.

1. Davis, Gary (1988). *The Sound Reinforcement Handbook*. Yamaha. p. 22. ISBN 0881889008.

1. Chinn, H. A.; Gannett, D. K.; Moris, R. M. (January 1940). ["A New Standard Volume Indicator and Reference Level"](http://www.aes.org/aeshc/pdf/chinn_a-new-svi.pdf). *Proceedings of the Institute of Radio Engineers*. **28** (1): 1–17. [doi:10.1109/JRPROC.1940.228815](https://doi.org/10.1109/JRPROC.1940.228815). [S2CID 15458694](https://api.semanticscholar.org/CorpusID:15458694). [Archived](https://web.archive.org/web/20120213001201/http://www.aes.org/aeshc/pdf/chinn_a-new-svi.pdf) 2012-02-13 at the Wayback Machine. Retrieved 2012-08-04.

## External links

- [The dBm calculator for impedance matching](http://www.sengpielaudio.com/calculator-volt.htm)
- [Convert dBm to watts](http://cgi.www.telestrian.co.uk/cgi-bin/www.telestrian.co.uk/dBm.pl)

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Adapted from the Wikipedia article [DBm](https://en.wikipedia.org/wiki/DBm) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/DBm?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.