Boonton 52000 Series USB CW Power Sensor - Manual (Page 58)

5 Other Information
What is a dBm?
When one of the powers is defined, again for convenience, as 1mW,
then the related unit, abbreviated to ‘dBm’, is described as follows.
The table below gives some powers and their equivalent dBm values:
Power dBm
1 μW -30.00
10 μW -20.00
100 μW -10.00
0.25 mW -6.02
0.5 mW -3.01
1 mW 0
2 mW 3.01
4 mW 6.02
10 mW 10.00
100 mW 20.00
1 W 30.00