db gain calculator

What is dB gain?

Decibel gain (dB gain) is a logarithmic way to describe how much a signal changes between an input and an output. Instead of saying “the signal got 100 times larger,” engineers often express that change in decibels because it is compact, intuitive once learned, and convenient for chaining multiple stages together.

A positive dB value means amplification (gain), while a negative dB value means attenuation (loss). A value of 0 dB means no change.

Core formulas used in this calculator

For power ratios

Use this when you are directly comparing power quantities (W, mW, etc.):

Gain(dB) = 10 × log10(Pout / Pin)

For voltage or current ratios

Use this for voltage or current only when source and load impedance are the same:

Gain(dB) = 20 × log10(Vout / Vin)

Gain(dB) = 20 × log10(Iout / Iin)

Inverse formulas

• Output = Input × 10^(Gain/N)
• Input = Output ÷ 10^(Gain/N)
• N = 10 for power, N = 20 for voltage/current

How to use the dB gain calculator

• Select Signal type: power or voltage/current.
• Choose what you want to solve for in Calculation mode.
• Enter the two required values.
• Click Calculate.

The result includes both dB gain and the equivalent linear ratio whenever relevant.

Quick dB reference table

dB	Power ratio	Voltage/Current ratio	Rule of thumb
+3 dB	~2.00×	~1.41×	About double power
+6 dB	~3.98×	~2.00×	About double voltage/current
+10 dB	10×	~3.16×	Ten times power
+20 dB	100×	10×	Ten times voltage/current
-3 dB	~0.50×	~0.71×	Half power point

Real-world examples

Audio preamp stage

If a preamp raises 0.1 V to 1 V with matched impedance, voltage gain is: 20 × log10(1 / 0.1) = 20 dB.

RF link power change

If transmitted power changes from 50 mW to 200 mW: 10 × log10(200 / 50) = 6.02 dB.

Attenuator

A -10 dB attenuator on 2 V input yields: 2 × 10^(-10/20) ≈ 0.632 V.

Common mistakes to avoid

• Using 20 log for power values (should be 10 log).
• Using voltage formula when impedances are not equal.
• Entering zero or negative levels (logarithms require positive ratios).
• Mixing units (e.g., input in mW, output in W) without conversion first.

FAQ

Can dB gain be negative?

Yes. Negative dB means the output is lower than input (signal loss).

Why are decibels useful?

They compress very large numeric ranges and make cascaded systems easier: gains in dB add directly.

Does 0 dB mean no signal?

No. It means no change between input and output. Absolute levels require references like dBm, dBV, or dBu.