Editing DBm (section)

== 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.

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&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 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.

In general the relationship between the power level {{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.|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}}</ref>