dBm to Voltage Calculator: Convert Power to Volts

A dBm to voltage calculator converts power in dBm into an RMS voltage, provided you also specify the system impedance. Enter the power level and impedance in ohms; the calculator returns voltage in volts, along with the equivalent power in milliwatts.

Formula

dBm is a logarithmic measure of power referenced to 1 milliwatt. To convert it to voltage, first convert dBm to watts, then use the power relationship for a resistive load:

P(W) = 0.001 × 10^dBm/10

V_RMS = √(P × R) = √(0.001 × 10^dBm/10 × R)

• dBm is the power level in decibels relative to 1 mW.
• P is power in watts; the calculator’s second output shows the same power in milliwatts.
• R is the load or reference resistance in ohms.
• V_RMS is the root-mean-square voltage across that resistance, in volts.

The formula assumes power is dissipated in a resistance and that the entered impedance can be treated as a real resistance. For a purely resistive load, RMS voltage is the appropriate value for comparing power. In an AC system with complex impedance, phase and measurement conventions also matter; a simple resistance-only calculation may not describe the actual voltage.

Worked Example

Using the calculator defaults, the input power is 0 dBm and the impedance is 50 ohms.

1. Convert power to milliwatts: 10^0/10 = 1 mW.
2. Convert milliwatts to watts: 1 mW × 0.001 = 0.001 W.
3. Calculate RMS voltage: √(0.001 W × 50 Ω) = √0.05 = 0.223607 V.

The result is 0.223607 V RMS, or about 223.6 mV RMS, and the power output is 1.000000 mW. These are the calculator’s six-decimal results for the defaults.

How dBm and Voltage Are Related

Voltage is not determined by dBm alone. The same power delivered to different resistances requires different voltages: at a higher resistance, more voltage is needed to deliver the same power. That is why a dBm-to-voltage conversion always needs an impedance assumption or input.

For reference, 0 dBm means 1 mW, not 0 volts and not 0 watts. Each increase of 10 dB represents ten times the power; each increase of 3 dB is approximately twice the power. Voltage does not follow the same multiplier as power when resistance stays constant: doubling power increases RMS voltage by √2, about 1.414.

At 50 Ω, 0 dBm corresponds to approximately 0.224 V RMS. At 75 Ω, the same 1 mW corresponds to approximately 0.274 V RMS. Those numbers differ because the impedance differs, even though the dBm value is unchanged.

When to Use This Calculator

This conversion is useful when a specification gives power in dBm but a measurement instrument, signal source, or circuit calculation uses voltage. Radio-frequency systems often use reference impedances such as 50 Ω or 75 Ω, but you should use the impedance relevant to the particular point being measured—not simply assume one from the equipment category.

• For a voltage level from a power specification, enter the stated dBm and the specified load impedance.
• For a receiver or signal-generator comparison, check whether the stated level is available power, delivered power, or a voltage measured under a particular termination.
• For a quick sanity check, convert the dBm value to milliwatts first, then verify that the resulting voltage is plausible for the impedance.

The result is RMS voltage. For a sine wave, peak voltage is √2 times RMS voltage, and peak-to-peak voltage is 2√2 times RMS voltage. Those relationships do not apply as written to every waveform; for non-sinusoidal signals, the crest factor and waveform shape affect peak values.

Common Mistakes and Limits

• Leaving out impedance: There is no unique dBm-to-voltage answer without a resistance or suitable impedance assumption.
• Confusing dBm with dB: dBm is an absolute power level referenced to 1 mW. A plain dB value describes a ratio and needs a reference level before it can represent an absolute power.
• Mixing RMS and peak voltage: The formula gives RMS voltage. Do not compare it directly with a peak or peak-to-peak specification without converting consistently.
• Using the wrong termination: A voltage measured with a matched load can differ from an open-circuit voltage. Check how the source level and instrument are specified.
• Rounding too early: Convert power and calculate voltage using the full value, then round the displayed answer. Low power levels can produce small voltages, so units such as mV or µV may be easier to read.

The calculator accepts dBm values from −300 to 300 and positive impedance values. Those broad limits support ordinary calculations and avoid a zero or negative resistance, which would not produce a meaningful result in this formula. They do not certify that a real device can produce or tolerate the calculated voltage or power. For complex RF impedances, transmission lines, or a mismatch between source and load, use the relevant circuit or RF measurement method rather than treating impedance as a simple resistor.

Frequently Asked Questions

How do I convert dBm to volts?
Convert dBm to watts with P = 0.001 × 10^dBm/10, then calculate RMS voltage as √(P × R), where R is in ohms.

Can I convert dBm to voltage without knowing impedance?
No. dBm specifies power, while voltage depends on the load resistance or impedance. State the impedance used for the conversion.

What is 0 dBm in volts at 50 ohms?
0 dBm is 1 mW. Across 50 Ω, that is √(0.001 × 50), or about 0.224 V RMS.

Is dBm voltage RMS or peak?
dBm measures power, not voltage. This calculator derives RMS voltage for a resistive load. Convert separately if you need the peak or peak-to-peak voltage of a sine wave.

Why does 0 dBm not always equal the same voltage?
Because 0 dBm always represents 1 mW, but the voltage required to deliver 1 mW changes with the resistance. A 50 Ω and a 75 Ω load therefore give different RMS voltages.

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in p | Power | dBm | 0 | -300 | 300
in r | Impedance | ohm | 50 | 0.000001
out v | RMS voltage | V | sqrt(0.001 * 10^(p / 10) * r) | 6
out mw | Power | mW | 10^(p / 10) | 6