dBm
Understanding dBm
dBm is the universal language for expressing RF power levels. Unlike dB (which is a ratio), dBm is an absolute measurement: 0 dBm = 1 milliwatt in a specified impedance (usually 50 ohms). The logarithmic scale makes it easy to cascade gains and losses with simple addition.
Common dBm Values
| dBm | Power | Typical Source |
|---|---|---|
| +60 dBm | 1 kW | Broadcast transmitter |
| +50 dBm | 100 W | Radar transmitter |
| +40 dBm | 10 W | Cellular base station PA |
| +30 dBm | 1 W | Cell phone transmitter |
| +20 dBm | 100 mW | Wi-Fi access point |
| +10 dBm | 10 mW | Bluetooth, signal generator |
| 0 dBm | 1 mW | Reference level |
| -30 dBm | 1 uW | Strong received signal |
| -80 dBm | 10 pW | Weak Wi-Fi signal |
| -120 dBm | 1 fW | GPS satellite signal |
| -174 dBm/Hz | 4e-21 W/Hz | Thermal noise floor |
P_mW = 10^(dBm/10)
dBm to dBW: dBW = dBm - 30
dBm to Watts: P_W = 10^((dBm-30)/10)
Cascade: P_out (dBm) = P_in (dBm) + Gain (dB)
Example: -20 dBm + 30 dB gain = +10 dBm
Frequently Asked Questions
What does dBm mean?
dBm is an absolute power unit referenced to 1 milliwatt. 0 dBm equals exactly 1 mW. Positive dBm values are greater than 1 mW; negative values are less. It uses logarithmic notation so gains and losses in dB can be added directly to power levels in dBm.
How do you convert dBm to watts?
P(watts) = 10^((dBm - 30)/10). For example: 30 dBm = 10^0 = 1 watt. 0 dBm = 10^-3 = 1 milliwatt. -30 dBm = 10^-6 = 1 microwatt. You can also convert to milliwatts: P(mW) = 10^(dBm/10).
What is the difference between dBm and dBW?
Both are absolute power units: dBm references 1 milliwatt, dBW references 1 watt. They differ by exactly 30 dB: dBW = dBm - 30. Use dBm for circuit-level signals; dBW for satellite and high-power link budgets.