dBm, W and V converter (RF power, VSWR)
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KEY POINTS
dBm expresses power on a log scale referenced to 1 mW: 0 dBm = 1 mW, 30 dBm = 1 W and 60 dBm = 1 kW. 3 dB doubles power and 10 dB multiplies it by ten. A VSWR of 1.5 means a reflection coefficient of 0.2 and a return loss of 14 dB, with 4% of forward power reflected. On plasma tools, the matching network drives RF reflection close to zero.
Power and voltage unit conversion
VSWR, reflection coefficient and reflected power (plasma matching check)
RF generators on plasma tools (such as 13.56 MHz) monitor reflected power, and the matching network drives reflection close to zero. Residual reflection changes the effective power and shifts the process, and generator protection may cut the output.
Total gain and loss (adding dB)
dBm reference table (50 Ω)
| dBm | Power | Voltage (rms) |
|---|---|---|
| -30 dBm | 1 µW | 7.07×10⁻³ V |
| 0 dBm | 1 mW | 0.224 V |
| 10 dBm | 10 mW | 0.707 V |
| 20 dBm | 100 mW | 2.24 V |
| 30 dBm | 1 W | 7.07 V |
| 40 dBm | 10 W | 22.4 V |
| 50 dBm | 100 W | 70.7 V |
| 60 dBm | 1,000 W | 224 V |
| 70 dBm | 10,000 W | 707 V |
VSWR reference table
| VSWR | |Γ| | Return loss | Reflected power share | Mismatch loss |
|---|---|---|---|---|
| 1.1 | 0.048 | 26.4 dB | 0.23 % | 0.010 dB |
| 1.2 | 0.091 | 20.8 dB | 0.83 % | 0.036 dB |
| 1.5 | 0.200 | 14.0 dB | 4.00 % | 0.177 dB |
| 2.0 | 0.333 | 9.5 dB | 11.11 % | 0.512 dB |
| 3.0 | 0.500 | 6.0 dB | 25.00 % | 1.249 dB |
| 5.0 | 0.667 | 3.5 dB | 44.44 % | 2.553 dB |
dB versus dBm
dB expresses the ratio of two quantities on a log scale: 10·log₁₀ for power ratios and 20·log₁₀ for voltage ratios. dBm is an absolute value referenced to 1 mW: 0 dBm = 1 mW, 30 dBm = 1 W and 60 dBm = 1 kW. Remembering that 3 dB doubles power and 10 dB multiplies it by ten lets you add up amplifier gains and cable losses in your head.
In semiconductor equipment, the RF generators that create plasma deliver hundreds of watts to tens of kilowatts (about 54 to 75 dBm), and matching network and cable losses and reflected power control directly affect process repeatability. RF semiconductor evaluation (power amplifiers, LNAs) uses the same units for gain, noise figure and output power.
FAQ
How many watts is 60 dBm?
1,000 W (1 kW). Every 10 dB multiplies power by ten, starting from 0 dBm = 1 mW.
How much power is reflected at a VSWR of 2?
The reflection coefficient is 1/3, so about 11% of forward power is reflected, a return loss of about 9.5 dB.
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Last updated: October 23, 2026