This tool converts RF power values into dBm, dBW, watts, RMS and peak voltage, and current for a chosen system impedance, supporting RF engineering and EMC compliance testing work.
Convert RF Power Between dBm, Watts, and Voltage in Any System Impedance
This tool converts a single RF power or voltage input into every commonly reported RF unit — dBm, dBW, dBµW, watts, RMS/peak/peak-to-peak voltage, RMS current, dBmV, dBµV, and dBµA — for a given system impedance. RF and microwave engineers, EMC/EMI test technicians, and antenna/amplifier designers use it to move between the units their signal generators, spectrum analyzers, and EMI receivers each report in.
Entering Power Level and System Impedance
Enter the RF power in milliwatts (mW) and the system impedance Z₀ in ohms (Ω) — 50 Ω is standard for RF/microwave work, 75 Ω for cable and broadcast systems. The tool returns power in dBm, dBW, dBµW, and watts, plus RMS, peak, and peak-to-peak voltage, RMS current, and the logarithmic voltage/current scales dBmV, dBµV, and dBµA.
How dBm, Watts, Voltage, and Current Are Related
Power in dBm is defined against a 1 milliwatt reference, per NIST Special Publication 811’s treatment of logarithmic power ratios:
$$P_{dBm} = 10 \log_{10}\left(\frac{P_{mW}}{1\text{ mW}}\right)$$
Shifting the reference by a fixed number of decades gives $P_{dBW} = P_{dBm} – 30$ and $P_{dB\mu W} = P_{dBm} + 30$, since 1 W = 1,000 mW and 1 mW = 1,000,000 µW.
Voltage and current follow from Ohm’s/Joule’s law, $P = V^2/Z_0$, applied to the system impedance:
$$V_{rms} = \sqrt{P \times Z_0} \qquad V_{peak} = V_{rms}\sqrt{2} \qquad V_{pp} = 2\,V_{peak} \qquad I_{rms} = \frac{V_{rms}}{Z_0}$$
The logarithmic voltage and current scales used on EMI receivers and CISPR-16-compliant test equipment are then referenced to 1 mV/1 µV/1 µA:
$$dB\mu V = 20 \log_{10}\left(\frac{V_{rms}\,[\mu V]}{1\,\mu V}\right) \qquad dB\mu A = 20 \log_{10}\left(\frac{I_{rms}\,[\mu A]}{1\,\mu A}\right)$$
The input mistake that causes the most confusion: dBm, dBW, and dBµW are power ratios and carry no impedance information, so they don’t change when Z₀ is edited. dBmV, dBµV, dBµA, and the voltage outputs are derived through $V = \sqrt{P \times Z_0}$, so they shift with every change to Z₀. Leaving Z₀ at the 50 Ω default while converting a value actually measured on a 75 Ω cable/CATV line silently introduces about a 1.76 dB error in every voltage-based output, even though the dBm figure stays correct.
Three errors that follow from this:
- Using the wrong Z₀ for the system the value was actually measured on (50 Ω RF vs. 75 Ω cable/broadcast), which only affects the voltage/current-based outputs.
- Reading the RMS voltage output as if it were peak or peak-to-peak — for example, setting a generator’s amplitude in Vpp using a number meant for Vrms, a factor-of-$2\sqrt{2}$ error.
- Treating dBµV and dBm as the same number with a different label. They’re referenced to different quantities (1 µV vs. 1 mW), so a high dBµV reading isn’t automatically a high dBm reading.
Power, Voltage, and Current Across a Matched Load
Standard Conversion Constants at 50 Ω
Derived from the formulas above at the RF-industry-standard Z₀ = 50 Ω. These offsets do not apply at other impedances — see the input-mistake note above.
| dBm | Power | V (RMS) | dBmV | dBµV | dBµA |
|---|---|---|---|---|---|
| 0 dBm | 1 mW | 223.6 mV | 47.0 | 107.0 | 73.0 |
| 10 dBm | 10 mW | 707.1 mV | 57.0 | 117.0 | 83.0 |
| 20 dBm | 100 mW | 2.236 V | 67.0 | 127.0 | 93.0 |
Common Questions About RF Power Conversion
Why does changing the system impedance change voltage but not dBm?
dBm is a power ratio referenced to 1 mW and has no impedance term. Voltage is derived from power through $V = \sqrt{P \times Z_0}$, so it moves whenever Z₀ changes even though the power hasn’t.
What’s the difference between RMS, peak, and peak-to-peak voltage?
RMS is the effective heating value of the waveform. Peak is $V_{rms}\sqrt{2}$ for a sine wave, and peak-to-peak is double the peak. Mixing them up is a common ~9 dB-equivalent sizing error.
Why do dBµV and dBm use different reference numbers?
dBm references 1 mW of power; dBµV references 1 µV of voltage. They describe the same physical signal from two different reference points, so converting between them requires knowing Z₀.
Can I use this calculator for 75 Ω cable or CATV systems?
Yes — set Z₀ to 75 Ω. dBm, dBW, and dBµW stay correct regardless of Z₀, but every voltage- and current-based output (dBmV, dBµV, dBµA, Vrms, Vpk) will shift accordingly.
Where does the 107 dBµV = 0 dBm figure come from?
At 0 dBm (1 mW) into 50 Ω, $V_{rms} = \sqrt{0.001 \times 50} \approx 223.6\,\text{mV} = 223{,}607\,\mu V$, which is 107.0 dBµV — the fixed offset used on CISPR-16-based EMI receivers.