FREE ENGINEERING CALCULATOR · BILINGUAL
dBm to Watts & Voltage Calculator: W, mW, Vrms, Vpp
Convert between dBm, watts and RMS voltage, then calculate sine-wave peak voltage, peak-to-peak voltage and RMS current. Supports 50 Ω, 75 Ω or a custom resistive load.
Enter parameters
Or load an example:
Calculated results
Parameters changed. Select Calculate to update the results.
| Power level | 0 dBm |
|---|---|
| Average power | 0.001 W |
| Average power (milliwatts) | 1 mW |
| RMS voltage | 0.223606798 V |
| Sine peak voltage | 0.316227766 V |
| Sine peak-to-peak voltage | 0.632455532 V |
| RMS current | 0.00447213595 A |
Power is average power delivered to the load; voltage is measured across that load. Vpeak and Vpp assume a sine wave with no DC offset.
Calculation formulas
P(W) = 10^((dBm − 30)/10) · dBm = 10 log₁₀(P/0.001 W) · Vrms = √(PR) · Vpp = 2√2 Vrms
Why does voltage conversion need impedance?
dBm references 1 mW, so conversion to watts does not depend on impedance. Voltage does: 1 mW gives about 0.223607 V RMS across 50 Ω and 0.273861 V RMS across 75 Ω. This calculator uses a pure resistance; complex loads require an actual real-power calculation.
What is the difference between dB and dBm?
dB is a ratio; dBm is an absolute power level referenced to 1 mW. A 10 dB attenuator reduces power to one tenth. For example, 20 dBm through an ideal 10 dB attenuator becomes 10 dBm, or 10 mW.
Why is Vpp not twice Vrms?
A sine wave peaks at √2 times RMS, so peak-to-peak is 2√2 times RMS. Square waves and modulated signals have different crest factors. For a pure resistor, P = Vrms²/R still applies to any waveform when its true RMS voltage is known.
Why might a generator display differ by a factor of two?
A generator may display amplitude for a specified termination. Changing the load changes terminal voltage; a high-impedance measurement differs from a matched load. This tool does not model source resistance, transmission-line reflections or mismatch loss; use the actual load conditions.
Quick reference
50 Ω resistive load, sine wave with no DC offset.
| dBm | W | Vrms (V) | Vpp (V) |
|---|---|---|---|
| -30 | 1.0e-6 | 0.00707106781 | 0.02 |
| -20 | 1.0e-5 | 0.0223606798 | 0.0632455532 |
| -10 | 0.0001 | 0.0707106781 | 0.2 |
| 0 | 0.001 | 0.223606798 | 0.632455532 |
| 10 | 0.01 | 0.707106781 | 2 |
| 20 | 0.1 | 2.23606798 | 6.32455532 |
| 30 | 1 | 7.07106781 | 20 |
| 40 | 10 | 22.3606798 | 63.2455532 |