About this tool
dBm expresses power on a logarithmic scale referenced to one milliwatt. Zero dBm equals 1 mW, positive dBm values are greater than 1 mW, and negative values are less than 1 mW.
The logarithmic form is convenient because gains and losses in dB can be added or subtracted directly from dBm power levels. This converter moves between dBm and milliwatts.
How to use it
- Choose dBm to mW or mW to dBm.
- Enter the value.
- Calculate and use the converted result with the same precision appropriate for your measurement or equipment specification.
Example: -3 dBm
-3 dBm is approximately 0.501 mW. A 3 dB reduction represents roughly half the power, which is why -3 dBm is close to half of the 1 mW reference.
Engineering notes
- dB is a ratio; dBm is an absolute power level referenced to 1 mW. Do not treat them as interchangeable units.
- Optical receive levels often use negative dBm values because the received power is much less than one milliwatt.
Frequently asked questions
What is 0 dBm in milliwatts?
Exactly 1 mW.
What is 10 dBm?
10 dBm is 10 mW.
Why is the scale logarithmic?
It lets very large power ratios be expressed compactly and makes cascaded gain/loss calculations easier.