dB & dBm Converter – Decibel Power, Voltage & Gain Calculator

System Impedance (Ω)

Used for voltage ↔ power conversion.

Absolute Power dBm / dBW

Enter any power value to convert between dBm, dBW, and linear power units.

dBm (decibel-milliwatt)

dBW (decibel-watt)

Watts (W)

Milliwatts (mW)

Microwatts (µW)

Nanowatts (nW)

Picowatts (pW)

RMS Voltage V / dBV

Calculated from power at the selected system impedance. Enter any voltage to sync.

Volts RMS (V)

Millivolts RMS (mV)

Microvolts RMS (µV)

dBV (decibel-volt)

dBµV (decibel-microvolt)

dB & dBm Guide

What is a Decibel (dB)?

A decibel (dB) is a dimensionless, logarithmic unit that expresses the ratio between two quantities. For power: dB = 10 × log₁₀(P₂/P₁). For voltage: dB = 20 × log₁₀(V₂/V₁).

What is dBm?

dBm is an absolute power unit referenced to 1 milliwatt: dBm = 10 × log₁₀(P / 1 mW). 0 dBm = 1 mW, 30 dBm = 1 W.

Voltage Conversion & Impedance

Power and RMS voltage are related by impedance (R): P = V² / R. For 50 Ω: 0 dBm ≈ 223.6 mV RMS.

Gain and Loss

3 dB power gain = power doubled. 6 dB voltage gain = voltage doubled. 20 dB voltage gain = ×10 voltage.

Quick Reference: Common dBm Values

dBm	Power	V RMS @ 50 Ω
−30 dBm	1 µW	7.07 mV
−20 dBm	10 µW	22.4 mV
−10 dBm	100 µW	70.7 mV
0 dBm	1 mW	223.6 mV
+10 dBm	10 mW	707 mV
+20 dBm	100 mW	2.236 V
+30 dBm	1 W	7.07 V
+40 dBm	10 W	22.4 V

Frequently Asked Questions

Can I convert dBm to dB?

Not directly. dBm is absolute, dB is relative. The difference between two dBm values is in dB.

What impedance should I use?

50 Ω for RF/microwave, 75 Ω for cable TV, 600 Ω for audio. Impedance only affects voltage conversion.

Why does 3 dB equal a 2× power ratio?

Because 10 × log₁₀(2) ≈ 3.01 dB. The −3 dB point is the half-power point for amplifiers and filters.

Power Gain / Loss Power dB

Enter a dB value or a power ratio to convert between the two.

Power Gain/Loss (dB)

Power Ratio (Pout / Pin)

Voltage Gain / Loss Voltage dB

Enter a dB value or a voltage ratio to convert between the two.

Voltage Gain/Loss (dB)

Voltage Ratio (Vout / Vin)

Gain and Loss

Power dB

dB = 10 × log₁₀(P_out / P_in)
Ratio = 10^dB/10

Voltage dB

dB = 20 × log₁₀(V_out / V_in)
Ratio = 10^dB/20

Key dB ↔ Ratio Values

dB	Power Ratio	Voltage Ratio
−20 dB	0.01×	0.1×
−10 dB	0.1×	0.316×
−6 dB	0.25×	0.5×
−3 dB	0.5×	0.707×
0 dB	1× (unity)	1× (unity)
+3 dB	2×	1.414×
+6 dB	4×	2×
+10 dB	10×	3.162×
+20 dB	100×	10×
+40 dB	10,000×	100×