dBm is an abbreviation for the dB referenced to one milliwatt.
Note 1: dBm is used in communication work as a measure of absolute power values. Zero dBm equals one milliwatt. A 3 dBm increase represents roughly doubling the power, which means that 3 dBm equals 2 milliwatt. For a 3 dBm decrease the power is reduced by one half, making -3 dBm equal to 0.5 milliwatt. To express an arbitrary power P as 
, or go in the other direction, the equations 
and 
, respectively, should be used. Below is table summarizing useful cases:
| 40 dBm | 10 watts
|
| 36 dBm | 4 watts
|
| 30 dBm | 1 watts
|
| 27 dBm | 500 milliwatts
|
| 26 dBm | 400 milliwatts
|
| 25 dBm | 320 milliwatts
|
| 24 dBm | 250 milliwatts
|
| 23 dBm | 200 milliwatts
|
| 22 dBm | 160 milliwatts
|
| 21 dBm | 130 milliwatts
|
| 20 dBm | 100 milliwatts
|
| 15 dBm | 32 milliwatts
|
| 10 dBm | 10 milliwatts
|
| 5 dBm | 3.2 milliwatts
|
| 4 dBm | 2.5 milliwatts
|
| 3 dBm | 2.0 milliwatts
|
| 2 dBm | 1.6 milliwatts
|
| 1 dBm | 1.3 milliwatts
|
| 0 dBm | 1.0 milliwatts
|
Note 2: In DOD practice, unweighted measurement is normally understood, applicable to a certain bandwidth, which must be stated or implied.
Note 3: In European practice, psophometric weighting may be implied, as indicated by context; equivalent to dBm0p , which is preferred.
See also
Zero dBm transmission level point
Source
