dBm to Watts Calculator

Convert between dBm, dBW and watts, milliwatts or microwatts — and the RMS, peak and peak-to-peak voltage that power makes across a 50 Ω (or any) load. Enter whichever you know.

Last updated 22 Sep 2026

dBm, watts and volts

dBm ⇄ W ⇄ dBW ⇄ volts

What do you know?Fill in that field; the others are locked and show the converted values.

Power (dBm)

Power

Power unit

Power (dBW)

RMS voltage

Voltage unit

Load impedance (Ω, resistive)50 Ω for most RF and test equipment, 75 Ω for video and cable TV, 600 Ω for old audio lines.

The power delivered into a resistive load of the impedance you entered, with the RMS voltage a meter would read across it. The dots show the size of the RMS current; a real RF current alternates millions of times a second.

100mWExample

+20 dBm into 50 Ω

dBm, watts and volts

P = 1 mW × 10^dBm/10; dBm = 10 log₁₀(P ÷ 1 mW) = dBW + 30; V_RMS = √(P × Z); V_pp = 2√2 × V_RMS

dBm: decibels relative to one milliwatt; 0 dBm = 1 mW, 30 dBm = 1 W
dBW: decibels relative to one watt; dBW = dBm − 30
Z: the load resistance the power is delivered into
dBµV: voltage level relative to 1 µV: 20 log₁₀(V_RMS ÷ 1 µV)

Worked example

+20 dBm into 50 Ω
P = 1 mW × 10^20/10 = 1 mW × 100 = 100 mW = −10 dBW
V_RMS = √(0.1 × 50) = √5 = 2.236 V
Peak = 3.162 V; peak-to-peak = 6.325 V
Current = 2.236 V ÷ 50 Ω = 44.72 mA; level = 126.99 dBµV

Common power levels into 50 Ω

Computed with this page’s formulas. Every 10 dB is a factor of 10 in power and √10 ≈ 3.16 in voltage; every 3 dB is about a factor of 2 in power.
dBm	dBW	Power	RMS voltage	Peak-to-peak (sine)
−100 dBm	−130 dBW	0.1 pW	2.236 µV	6.325 µV
−80 dBm	−110 dBW	10 pW	22.36 µV	63.25 µV
−60 dBm	−90 dBW	1 nW	223.6 µV	632.5 µV
−40 dBm	−70 dBW	100 nW	2.236 mV	6.325 mV
−30 dBm	−60 dBW	1 µW	7.071 mV	20 mV
−20 dBm	−50 dBW	10 µW	22.36 mV	63.25 mV
−10 dBm	−40 dBW	100 µW	70.71 mV	200 mV
0 dBm	−30 dBW	1 mW	223.6 mV	632.5 mV
+3 dBm	−27 dBW	1.995 mW	315.9 mV	893.4 mV
+10 dBm	−20 dBW	10 mW	707.1 mV	2 V
+13 dBm	−17 dBW	19.95 mW	998.8 mV	2.825 V
+20 dBm	−10 dBW	100 mW	2.236 V	6.325 V
+27 dBm	−3 dBW	501.2 mW	5.006 V	14.16 V
+30 dBm	0 dBW	1 W	7.071 V	20 V
+33 dBm	+3 dBW	1.995 W	9.988 V	28.25 V
+37 dBm	+7 dBW	5.012 W	15.83 V	44.77 V
+40 dBm	+10 dBW	10 W	22.36 V	63.25 V
+47 dBm	+17 dBW	50.12 W	50.06 V	141.6 V
+50 dBm	+20 dBW	100 W	70.71 V	200 V
+60 dBm	+30 dBW	1 kW	223.6 V	632.5 V

What dBm means

Radio and test engineers measure power in decibels because the levels they deal with span enormous ranges: a transmitter may put out 100 W while the receiver at the other end works with a tenth of a picowatt. A decibel scale turns multiplication into addition. dBm is the power relative to one milliwatt: 0 dBm is 1 mW, +10 dBm is 10 mW, +20 dBm is 100 mW, +30 dBm is 1 W, and −30 dBm is 1 µW. Each 10 dB is a factor of ten, and each 3 dB almost exactly a factor of two (10 log₁₀ 2 = 3.01 dB). dBW works the same way relative to one watt, so dBW = dBm − 30.

Why decibels are convenient. Gains and losses add. A +20 dBm signal generator feeding a cable with 3 dB of loss and a 10 dB attenuator delivers +7 dBm; an amplifier with 15 dB of gain brings it to +22 dBm. Only the final answer needs converting back to watts.

Power and voltage. A power level becomes a voltage only once you know the resistance it is delivered into. In a 50 Ω system 0 dBm is 223.6 mV RMS, or 632.5 mV peak-to-peak on an oscilloscope, for a sine wave; +20 dBm is 2.236 V RMS. In 75 Ω, 0 dBm is 273.9 mV; in 600 Ω, the old audio reference, it is 774.6 mV, which is why that figure appears on audio meters. Voltage goes with the square root of power, so each 10 dB multiplies the voltage by √10 ≈ 3.16 and each 20 dB by ten. EMC and receiver work often quote voltage levels in dBµV instead, which the page also shows.

Peak voltage matters for parts. The peak of a sine wave is √2 times its RMS value, and a modulated signal (a multi-carrier or OFDM signal, for instance) can peak several times higher again for the same average power. Capacitors, switches and amplifier stages must handle the peak, not the average. For matching a source to a load of a different resistance, see the L-network calculator; for the basic V, I, R and P relations, the Ohm’s law calculator.

Frequently asked questions

How do I convert dBm to watts?

P (W) = 10^((dBm − 30) ÷ 10). +20 dBm = 10^(−1) W = 0.1 W; +30 dBm = 1 W; +40 dBm = 10 W.

How do I convert watts to dBm?

dBm = 10 × log10(P in mW) = 10 × log10(P in W) + 30. 5 W is 10 × log10(5000) = 36.99 dBm.

What voltage is 0 dBm?

It depends on the impedance. Into 50 Ω, 223.6 mV RMS; into 75 Ω, 273.9 mV; into 600 Ω, 774.6 mV.

What is the difference between dBm and dBW?

The reference: dBm is relative to 1 mW and dBW to 1 W. They differ by exactly 30: 0 dBW = +30 dBm = 1 W.

Is 3 dB double the power?

Very nearly: 3 dB is a factor of 10^0.3 = 1.9953. Exactly double is 3.01 dB.

Related calculators

References

ITU-R Recommendation V.574. Use of the decibel and the neper in telecommunications (dBm, dBW and related units).
IEC 60027-3. Letter symbols to be used in electrical technology — Part 3: Logarithmic and related quantities, and their units.
Horowitz P, Hill W. The Art of Electronics, 3rd ed. Cambridge University Press, 2015: decibels, RMS and peak values.