Op-Amp Gain Calculator
Find the voltage gain of an inverting or non-inverting op-amp from its feedback and input resistors, in V/V and decibels.
How it works
Non-inverting: A = 1 + Rf ÷ Rin · Inverting: A = −Rf ÷ Rin · Gain(dB) = 20 × log₁₀|A|
An ideal op-amp with negative feedback sets its gain purely from the two resistors, not the amplifier itself. The non-inverting configuration always has a gain of at least 1 and keeps the input signal’s polarity, while the inverting configuration flips the sign and can have a gain below 1. Expressing the gain in decibels (20·log₁₀ of the ratio, since it is a voltage ratio) makes it easy to add up stages.
Worked example
A non-inverting amp with Rf = 100 kΩ and Rin = 10 kΩ has a gain of 1 + 100 ÷ 10 = 11 V/V, or 20·log₁₀(11) = 20.8 dB. A 100 mV input becomes 1.1 V at the output.
Frequently asked questions
What is the difference between inverting and non-inverting gain?
Non-inverting gain is 1 + Rf/Rin and preserves polarity, so its minimum is 1×. Inverting gain is −Rf/Rin, flipping the signal, and it can be less than 1 for attenuation. The non-inverting input also presents a much higher input impedance.
Why is the gain independent of the op-amp?
With plenty of open-loop gain and negative feedback, the amplifier works to keep its two inputs equal, which forces the output to whatever the resistor ratio dictates. This makes the closed-loop gain stable and predictable across temperature and part variation.
Is there a limit to how much gain I can set?
Yes — the real op-amp’s gain-bandwidth product caps useful gain at high frequencies, and very high gains amplify noise and offset. In practice you cascade moderate-gain stages rather than asking one stage for a gain of thousands.
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This calculator is for educational purposes. Double-check important results before acting on them.