View source for Decibel watt

{{short description|SI measurement of signal strength and intensity}}
{{Redirect|DBW}}

The '''decibel watt''' ('''dBW''' or '''dB<sub>W</sub>''') is a unit for the measurement of the strength of a signal expressed in [[decibel]]s relative to one [[watt]]. It is used because of its capability to express both very large and very small values of power in a short range of number; e.g., 1&nbsp;milliwatt = −30&nbsp;dBW, 1&nbsp;watt = 0&nbsp;dBW, 10&nbsp;watts = 10&nbsp;dBW, 100&nbsp;watts = 20&nbsp;dBW, and 1,000,000&nbsp;W = 60&nbsp;dBW.

:<math>\mbox{Power in dBW} = 10 \log_{10}\frac{\mbox{Power}}{ 1 \mathrm{W}} </math>

and also

:<math>\mbox{Power in W} = 10^{\frac{\mbox{Power in dBW}}{10}} </math>

Compare dBW to [[dBm]], which is referenced to one milliwatt (0.001&nbsp;W).

A given dBW value expressed in dBm is always 30 more because 1 watt is 1,000 milliwatts, and a ratio of 1,000 (in power) is 30&nbsp;dB; e.g., 10&nbsp;dBm (10&nbsp;mW) is equal to −20&nbsp;dBW (0.01&nbsp;W).

In the [[SI]] system the non SI modifier [[decibel]] (dB) is not permitted for use directly alongside [[SI]] units so the dBW is not directly permitted but 10 dBW may be written 10 dB (1 watt).<ref>{{Cite journal|last=Thompson|first=E Ambler|last2=Taylor|first2=Barry N|date=2008|title=Guide for the use of the International System of Units (SI)|journal=NIST Special Publication|volume=811|at=p. 30|doi=10.6028/nist.sp.811e2008|doi-access=free}}</ref>{{rp|7.4}}

== See also ==
*[[dBm]]

== References ==
{{reflist}}

{{decibel}}

[[Category:Sound]]
[[Category:Units of power]]
[[Category:Logarithmic scales of measurement]]


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