Inverting Op-Amp Gain Calculator

This inverting op-amp gain calculator gives the closed-loop voltage gain of an inverting amplifier built from an operational amplifier with two resistors. Enter the feedback resistor and the input resistor and the calculator returns the gain, which is minus the feedback resistor divided by the input resistor, plus the output for an input voltage you choose. The minus sign means the output is inverted, flipped in polarity, relative to the input. This simple resistor ratio is one of the most used op-amp configurations in analogue electronics. The formula, a worked example and the assumptions are below.

Feedback resistor Rf (\u03A9)

Input resistor Rin (\u03A9)

Input voltage Vin (V)

Gain magnitude

Output voltage

The formula

The gain of an inverting amplifier is Av = minus Rf / Rin, where Rf is the feedback resistor and Rin the input resistor. The output is Vout = Av times Vin, inverted relative to the input.

Worked example

With a 10 k feedback resistor and a 1 k input resistor, the gain is minus 10000/1000 = minus 10, so a 0.5 V input gives a minus 5 V output. Enter 10000, 1000, 0.5 to confirm.

Frequently asked questions

What sets the gain of an inverting amplifier?

The ratio of the feedback resistor to the input resistor, with a minus sign: Av = minus Rf / Rin.

Why is the gain negative?

The configuration inverts the signal, so the output swings opposite to the input. The magnitude is Rf over Rin.

Does the op-amp itself affect the gain?

For an ideal op-amp with enough open-loop gain, only the resistors set the closed-loop gain.

Who this calculator is for

This calculator is for electronics students, hobbyists and engineers.

What this calculator assumes

You enter values in the units shown.
Ideal components are assumed.
Results are rounded for display.

Formula and sources

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