dBm

A power level of 0 dBm corresponds to a power of 1 milliwatt. A 10 dB increase in level 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 {{mvar|P}} in mW as {{mvar|x}} in dBm, the following expression may be used:{{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}}

$$\backslash begin\{align\}$$

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

\end{align}

Conversely, to express an arbitrary power level {{mvar|x}} in dBm, as {{mvar|P}} in mW:

$$\backslash begin\{align\}$$

P &= 1~\text{mW} \cdot 10^{\frac{x}{10}}

\end{align}

Below is a table summarizing useful cases:

{{Main|Orders of magnitude (power)}}

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, unweighted measurement is normally understood, applicable to a certain bandwidth, which must be stated or implied.

In European practice, psophometric weighting may be, as indicated by context, equivalent to dBm0p, which is preferred.

In audio, 0 dBm often corresponds to approximately 0.775 volts, since 0.775 V dissipates 1 mW in a 600 Ω load. The corresponding voltage level is 0 dBu, 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.

In general the relationship between the power level {{mvar|P}} in dBm and the 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:

$$\backslash begin\{align\}$$

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 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{{cite book|last=Davis|first=Gary|title=The Sound Reinforcement Handbook|year=1988|publisher=Yamaha|isbn=0881889008|pages=22}} in 1940.{{cite journal|last=Chinn|first=H. A.|author2=D. K. Gannett|author3=R. M. 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}}

• Decibel watt
• dBm0

{{FS1037C MS188}}

{{reflist}}

• [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