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What are dBm and dBW respectively? Print
May 2010

According to Wikipedia as at 17 May 2010 (, dBm is an abbreviation for the power ratio of the measured power referenced to one milliwatt (mW). It is used in radio, microwave and fiber optic networks as a convenient measure of absolute power because of its capability to express both very large and very small values in a short form. 

To express an arbitrary power P in Watt as x dBm, the following equation may be used:  x = 10 log10 (1000P)

Some examples: Zero dBm equals one milliwatt. A 3 dB increase represents roughly doubling the power, which means that 3 dBm equals roughly 2 mW. For a 3 dB decrease, the power is reduced by about one half, making −3 dBm equal to about 0.5 milliwatt. 

dBW is referenced to one watt (1000 mW). 

By comparison, the decibel (dB) is a dimensionless unit, used for quantifying the ratio between two values, such as signal-to-noise ratio.