Engineering Reference

RF Power dBm, Watt and Voltage Reference

Quick-reference RF power conversions between dBm, dBW, watts and milliwatts, with impedance-qualified RMS, peak, peak-to-peak voltage, current, ratios and link-budget terms.

Reading Time: 13 min
Format: RF power lookup
Updated: September 26, 2026

Quick RF Power Lookup

RF power quantity lookup
Need to know	Use	Required condition
Absolute linear power	W, mW or µW	State the measurement reference plane
Absolute logarithmic power	dBm or dBW	Keep the 1 mW or 1 W reference
Gain or loss	dB	State direction and sign convention
Voltage from power	Vrms = √(PR)	State impedance and RMS convention
Current from power	Irms = √(P/R)	Use a resistive or qualified impedance
Link result	Received power and link margin	Use consistent gains, losses and reference planes

RF Power Parameter Table

RF power parameter lookup
Parameter	Symbol	Unit	Meaning	Common boundary
Absolute RF power	P	W, mW, µW	Linear power delivered or available under stated conditions	Do not confuse power with voltage without impedance
Power level referenced to 1 mW	PdBm	dBm	10 log10(P / 1 mW)	dBm is absolute; dB alone is a ratio
Power level referenced to 1 W	PdBW	dBW	10 log10(P / 1 W)	dBm = dBW + 30
Power gain or loss	G, L	dB	Logarithmic power ratio	Sign convention and reference direction must be stated
Voltage	Vrms, Vpk, Vpp	V	Waveform voltage across a stated impedance	Always state RMS, peak or peak-to-peak
Current	Irms	A	RMS current associated with power and impedance	Requires a resistive or qualified impedance model
Reference impedance	R, Z0	Ω	Impedance used for power-voltage conversion	50 Ω is common, not universal
Transmit power	PT	dBm, W	Power at the specified transmitter reference plane	Clarify whether cable loss and antenna gain are included
Received power	PR	dBm, W	Power available at a specified receiver reference plane	Not identical to receiver sensitivity or margin
EIRP	EIRP	dBm, dBW	Transmitter power plus antenna gain minus pre-antenna losses	Gain must be referenced consistently, commonly dBi
Link margin	M	dB	Received power minus required receiver level	Keep all gains, losses and levels on one convention

dBm, dBW and Linear Power

dBm definition

dBm = 10 log10(P / 1 mW). In watts, P = 10^((dBm − 30)/10).

dBW definition

dBW = 10 log10(P / 1 W). Therefore dBm = dBW + 30.

Absolute versus relative

dBm and dBW are absolute levels. dB is a ratio. A gain or loss in dB may be added to a dBm level along one signal path.

Summing sources

Do not add independent dBm source powers directly. Convert each to watts, sum the linear powers, then convert the result back to dBm.

Common dBm power anchors
dBm	dBW	Linear power
-30 dBm	-60 dBW	1.000 µW
-20 dBm	-50 dBW	10.00 µW
-10 dBm	-40 dBW	100.0 µW
0 dBm	-30 dBW	1.000 mW
10 dBm	-20 dBW	10.00 mW
20 dBm	-10 dBW	100.0 mW
30 dBm	0 dBW	1.000 W
40 dBm	10 dBW	10.00 W
50 dBm	20 dBW	100.0 W
60 dBm	30 dBW	1000 W

Useful dB Power Ratios

Common decibel power ratios
Change	Power ratio	Engineering interpretation
+3.0103 dB	2×	Exact doubling, rounded casually to +3 dB
−3.0103 dB	0.5×	Exact halving
+10 dB	10×	One decade increase in power
−10 dB	0.1×	One decade decrease in power
+20 dB	100×	Two decades increase in power
−20 dB	0.01×	One percent of the original power

Power ratio = 10^(dB/10). A positive or negative sign has meaning only after the gain/loss direction is defined.

Power to Voltage and Current

For power dissipated in a resistive load, Vrms = √(PR) and Irms = √(P/R). For a sine wave, Vpk = √2 Vrms and Vpp = 2√2 Vrms.

Common RF voltage anchors
Power	Impedance	Vrms	Vpk	Vpp	Irms
0 dBm = 1 mW	50 Ω	0.2236 V	0.3162 V	0.6325 V	4.472 mA
0 dBm = 1 mW	75 Ω	0.2739 V	0.3873 V	0.7746 V	3.651 mA
10 dBm = 10 mW	50 Ω	0.7071 V	1.000 V	2.000 V	14.14 mA
20 dBm = 100 mW	50 Ω	2.236 V	3.162 V	6.325 V	44.72 mA
30 dBm = 1 W	50 Ω	7.071 V	10.00 V	20.00 V	141.4 mA

These voltage values assume sinusoidal steady-state power in a resistive load. Available power, incident-wave voltage, matched-load voltage and instrument display conventions can use different reference definitions.

Voltage Ratios and Impedance

Equal impedance

dB = 20 log10(V2/V1) follows from power being proportional to voltage squared when both voltages use equal impedance and compatible conventions.

Unequal impedance

Do not use 20 log10 of voltage ratio as a power ratio when impedances differ. Calculate P = Vrms²/R on each side and then use 10 log10 of the power ratio.

50 Ω is not universal

RF test systems commonly use 50 Ω; video and cable systems often use 75 Ω. Other source, load and complex impedances also occur.

RMS must be explicit

Power equations use RMS voltage and current for sinusoidal resistive-load examples. Peak and peak-to-peak values cannot be substituted directly.

Link-Budget Power Terms

RF link-budget power terminology
Term	Typical expression	Reference-plane check
EIRP	PT + GT − LTX	Transmitter output, pre-antenna losses and antenna gain must be located consistently
Received power	PT + GT + GR − all path/system losses	Specify whether connector and cable losses are included
Receiver sensitivity	Required input level for stated performance	Depends on bandwidth, modulation, coding, BER/PER and test conditions
Link margin	PR − sensitivity	Both quantities must use the same reference point and units
Friis result	Ideal free-space received power	Does not include obstruction, fading, mismatch, polarization or implementation loss unless added

Worked Reference Examples

dBm to watts

20 dBm = 10^((20−30)/10) = 0.1 W.

Watts to dBm

2 W = 10 log10(2000) ≈ 33.0103 dBm.

dBW relationship

10 dBW = 40 dBm = 10 W.

Power ratio

−6 dB → 10^(−6/10) ≈ 0.2512× power.

Equal-impedance voltage ratio

+6.0206 dB → 2× voltage when impedances are equal.

0 dBm in 50 Ω

√(0.001 × 50) = 0.2236 Vrms.

Simple signal path

20 dBm + 6 dB gain − 2 dB cable loss = 24 dBm at the stated output plane.

Independent power sum

0 dBm + 0 dBm sources = 1 mW + 1 mW = 2 mW ≈ 3.0103 dBm, assuming powers may be combined incoherently.

Common Interpretation Mistakes

Treating dB as an absolute power unit.
Confusing dBm with dBW.
Using 20 log10 for a power ratio.
Using 10 log10 for an equal-impedance voltage ratio.
Adding independent dBm powers directly.
Assuming 3 dB is an exact factor of two.
Converting power to voltage without impedance.
Assuming every RF system is 50 Ω.
Mixing RMS, peak and peak-to-peak voltage.
Using resistive-load equations for an unqualified complex impedance.
Mixing dBi and dBd antenna-gain references.
Applying cable loss with the wrong sign.
Mixing transmitter, antenna and receiver reference planes.
Treating receiver sensitivity as received power.
Assuming ideal Friis power guarantees a working link.

RF Power Lookup Workflow

1Identify whether the value is absolute power or a ratio.
2Confirm dBm, dBW, dB or linear units.
3Identify the measurement reference plane.
4Normalize source powers to watts before summing.
5Apply path gains and losses with a consistent sign convention.
6State impedance before converting power to voltage or current.
7State RMS, peak or peak-to-peak voltage.
8Check whether impedance is resistive, matched or complex.
9Keep antenna gain references consistent.
10Separate ideal propagation from practical losses.
11Preserve meaningful precision.
12Verify the result against a nearby power anchor.

Support reference

FAQ

What is dBm?

dBm is an absolute power level referenced to 1 milliwatt. Zero dBm equals 1 mW, 30 dBm equals 1 W and -30 dBm equals 1 µW.

What is the difference between dB and dBm?

dB expresses a logarithmic ratio. dBm expresses an absolute power level referenced to 1 mW. A standalone dB value needs a reference level before it becomes an absolute result.

What is the difference between dBm and dBW?

dBm uses 1 mW as its reference while dBW uses 1 W. Therefore dBm equals dBW plus 30.

How do I convert dBm to watts?

Use P(W) = 10^((dBm - 30)/10). For example, 20 dBm equals 0.1 W and 30 dBm equals 1 W.

How do I convert watts to dBm?

Use dBm = 10 log10(P(W) × 1000). Power must be positive.

Does 3 dB mean exactly twice the power?

A precise factor of two is 10 log10(2), approximately 3.0103 dB. The common 3 dB statement is a useful rounded approximation.

How do I convert dBm to voltage?

First convert dBm to watts, then use Vrms = √(PR) for a resistive load. The resistance and RMS convention must be stated.

What voltage is 0 dBm in 50 ohms?

Zero dBm is 1 mW. Across 50 Ω, that is approximately 0.2236 Vrms, 0.3162 V peak or 0.6325 V peak-to-peak for a sine wave.

Is 50 ohms universal in RF systems?

No. Fifty ohms is common in RF instrumentation and systems, but 75 Ω and other impedances are also used. Always use the applicable reference impedance.

When can I use 20 log10 for a voltage ratio?

Use 20 log10(V2/V1) when the compared voltages refer to equal impedances or when the transfer quantity is explicitly a voltage ratio. With unequal impedances, compute power first.

Can dBm values be added directly?

Independent source powers must be converted to linear power before summing. In a signal path, gains and losses in dB may be added to an absolute dBm level.

What is EIRP?

EIRP is transmitter output power plus antenna gain referenced to an isotropic radiator minus losses before the antenna, using consistent dB and dBm or dBW conventions.

What is link margin?

Link margin is the difference in dB between predicted received power and the required receiver level under the same reference convention.

Does received power alone guarantee a working RF link?

No. Required SNR, bandwidth, noise figure, modulation, interference, fading, polarization and implementation losses also matter.

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