Inverting Op-Amp Gain Calculator

Gain, output voltage and clipping for an inverting amplifier.

What it does

An inverting amplifier multiplies the input by −Rf / Rin. The output is flipped in sign and cannot go beyond the supply rails.

Where it's used

Audio and sensor gain stages, summing amplifiers and sign inversion.

How to use it

Enter Rin and Rf.
Enter the input voltage.
Enter the supply rails (±).
Check the output and whether it clips.

The formula explained

G: −Rf / Rin — voltage gain
Zin: input impedance = Rin
Vout: G × Vin, limited by the rails

Worked example

A ×21 inverting stage on ±15 V.

Inputs:

Input resistor Rin: 4.7k Ω
Feedback resistor Rf: 100k Ω
Input voltage: 0.2 V
Supply rails (±): 15 V

The calculator gives:

Voltage gain: -21.2766 V/V
Gain (dB): 26.56 dB
Output voltage: -4.255 V

Tips and common mistakes

The output cannot reach the rails exactly unless the op-amp is “rail-to-rail”.
Rin is also the input impedance — make sure the source can drive it.
High gain reduces bandwidth (gain-bandwidth product).

Questions people ask

How much bandwidth will my amplifier have?

Roughly the op-amp’s gain-bandwidth product divided by the noise gain, 1 + Rf / Rin. A ×21 inverting stage has a noise gain of about 22, so a 1 MHz op-amp gives around 45 kHz.

How do I add several signals together?

Give each input its own resistor into the same inverting input: Vout = −Rf × (V1/R1 + V2/R2 + …). With equal resistors the output is minus the sum of the inputs — the classic audio mixer.

Why is the output negative?

The input drives the inverting (−) terminal, so the output moves the opposite way. For AC signals this is just a 180° phase flip. If you need a positive output from a positive input, use a non-inverting stage or a second inverting stage.

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