What is the dB of 1 watt of power?

Question

Helping friend with homework.

Answer 1

Power expressed in dB is usually referenced to milliwatts, that is, in dBm. 1 watt of power is 1000 milliwats. To convert the power in milliwatts to dBm, use the formula:

   Power in dBm = 10 log (1000 mW) = 30 dBm.

Therefore, 1 watt = 30 dBm

Answer 2

dB is a ratio of powers.  1 watt is an absolute power, it has no ratio, therefore by itself it has no dB value.  If it is referenced to 1 watt (commonly used reference) it is 0 dBW (=10log(1))  Referenced to 1 milliwatt (also commonly used) it is +30 dBm (=10log(1000)).