URDB

Op-Amp Gain Calculator — inverting, non-inverting and differential

Gain and resistor selection for inverting, non-inverting, differential, summing and instrumentation amplifier topologies.

Example: Non-inverting with Rin = 1 kΩ and Rf = 10 kΩ gives a gain of 11 V/V (20.8 dB).

Formula

non-inverting: A = 1 + Rf/Rin    inverting: A = −Rf/Rin

Worked example

Non-inverting with Rin = 1 kΩ and Rf = 10 kΩ gives a gain of 11 V/V (20.8 dB).

  1. A = 1 + Rf / Rin

    A = 1 + 10 kΩ / 1 kΩ

    11 V/V

Frequently asked questions

How do I calculate op-amp gain?

For a non-inverting stage, 1 + Rf/Rin. For an inverting stage, −Rf/Rin. The minus sign means the output is inverted; the magnitude is what it says. A 10 kΩ feedback with a 1 kΩ input gives 11 non-inverting or −10 inverting.

What is noise gain and why does it differ?

Noise gain is 1 + Rf/Rin regardless of topology — it is the gain the feedback loop actually runs at, and it sets bandwidth and stability. An inverting stage with unity signal gain still has a noise gain of 2, so it gets half the bandwidth you might expect.

Why can't a non-inverting amplifier attenuate?

Because the formula is 1 + Rf/Rin, and Rf/Rin is never negative. The minimum is unity, with Rf shorted. To attenuate, put a divider before the amplifier or use an inverting stage, where Rf/Rin below 1 works fine.

How does gain limit bandwidth?

Op-amps have a fixed gain-bandwidth product, so bandwidth is GBW divided by noise gain. A 1 MHz part at a gain of 100 gives you 10 kHz. Two cascaded stages of gain 10 give the same overall gain with ten times the bandwidth.

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