Inverting Amplifier Calculator

Work out inverting amplifier instantly with clear inputs, formula shown and shareable results.

About Inverting Amplifier Calculator

An inverting amplifier has gain -Rf/Rin. Input impedance is just Rin, because the inverting input sits at a virtual earth. Bandwidth is set by the noise gain 1 + |Av|, not the signal gain, which is why a unity-gain inverter has half the bandwidth of a unity-gain follower.

Formula

Inverting gain

Av = -Rf / Rin; Zin = Rin; bandwidth = GBW / (1 + |Av|)

Worked example

With the default values below, Inverting Amplifier Calculator returns Voltage gain of -10.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Feedback resistor: 100,000 Ω
Input resistor: 10,000 Ω
Input voltage: 0.2 V
Op-amp gain-bandwidth product: 1 MHz

Results

Voltage gain: -10.00 x
Output voltage: -2.0000 V
Input impedance: 10,000.00 Ω
Closed-loop bandwidth: 90.91 kHz

Step by step

1Values used
2Inverting gain
3Voltage gain= -10.00 x
4Output voltage= -2.0000 V
5Input impedance= 10,000.00 Ω
6Closed-loop bandwidth= 90.91 kHz

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

Frequently Asked Questions

What is the virtual earth?

Feedback holds the inverting input at the same potential as the non-inverting input, so it behaves like a ground that draws no current from the source.

Why is input impedance only Rin?

Because the source sees Rin terminating at the virtual earth, unlike the non-inverting configuration where the source drives the op-amp input directly.