Convert power levels between Watts, dBW and dBm

The decibel watt (dBW) is a unit for the measurement of the strength of a signal expressed in decibels 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, eg 1 milliwatt = -30 dBW, 1 watt = 0 dBW, 10 watts = 10 dBW, 100 watts = 20 dBW and 1,000,000 W = 60 dBW.

dBm is referenced to one milliwatt (0.001 W). 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).

Enter one value (either in dBW, dBm or W) and click the “Convert” button next to it to calculate the two other values.

Power = 


Power = 


Power = 


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  1. I wish to use an excel spread sheet to calculate the total Insertion Loss over an entire coaxial cable where there will be 8 to 10 power dividers installed with antenna isolators to 8 to 10 antennas. The insertion loss for every connector, power divider, length of coaxial cable/100M will be entered into a sepearate cell and the total sum of dB will be calculated. I know my power required at the antenna is 4 Watts for an ERP of 6 Watts from a 0dBd antenna (maximum watts allowed in a Class IIA hazardous are). I need to convert the formula below to a useable formula in the excel spread sheet so I can enter it into each cell where it is the output to the on of 8 to 10 antennas. then I can determine the input Watts required and the attenuator at each of the antennas before the last one. Can you provide me with the formaula to insert into the excel spreadsheet?

    10 log10 PT/PR

    1. Hi Richard.
      I probably could, but I’m no Excel expert, so it would probably take me as long as it would take you!
      Good luck, however.

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