What is dBm?
dBm expresses power relative to 1 milliwatt on a logarithmic scale. 0 dBm is 1 mW, and every 10 dB is a factor of 10. It makes it easy to add gains and subtract losses in RF and fiber links.
P(dBm) = 10 × log₁₀(P in mW)
P(mW) = 10^(dBm ÷ 10)
dBW = dBm − 30
dBm to power table
| dBm | Power | Typical |
|---|---|---|
| −90 | 1 pW | Weak Wi-Fi / cellular signal |
| −67 | 0.2 nW | Minimum for reliable VoIP over Wi-Fi |
| −30 | 1 µW | Strong signal next to router |
| 0 | 1 mW | Fiber optic transmitter |
| 20 | 100 mW | Wi-Fi router transmit power |
| 30 | 1 W | Cell phone max, FRS/GMRS handheld |
| 37 | 5 W | CB radio |
| 50 | 100 W | HF amateur transceiver |
Frequently asked questions
How many watts is 30 dBm?
30 dBm equals 1 watt (1,000 mW).
What is a good Wi-Fi signal in dBm?
−30 to −50 dBm is excellent, −60 to −67 dBm is good for streaming and calls, and below −70 dBm is weak.
What is the difference between dB and dBm?
dB is a ratio (gain or loss). dBm is an absolute power level referenced to 1 mW.