The decibel watt or dBW is a unit for the measurement of the strength of a signal expressed in decibel

Decibel

The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...

s relative to one watt

Watt

The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...

. It is used because of its capability to express both very large and very small values of power in a short range of number, eg 1 milliwatt = -30 dBW, 1 watt = 0 dBW, 10 watts = 10 dBW, 100 watts = 20 dBW and 1,000,000 W = 60 dBW.


Compare dBm

DBm

dBm is an abbreviation for the power ratio in decibels of the measured power referenced to one milliwatt . 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...

, which is referenced to one milliwatt (0.001 W). Certain dBW value in dBm is always 30 more because 1 watt is 1000 milliwatts, and ratio of 1000 (in power) is 30 dB, eg 10 dBm (10mW) is equal to -20 dBW (0.01 W).

Although the decibel

Decibel

The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...

 (dB) is permitted for use alongside SI

Si

Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...

units, the dBW is not.