Inverting Op-Amp Gain Calculator

This inverting op-amp gain calculator works out the closed-loop voltage gain of an operational amplifier wired in the standard inverting configuration, one of the most common building blocks in analogue electronics, from audio preamps to sensor signal conditioning. You enter the feedback resistor (Rf), the input resistor (Rin), and an input voltage (Vin) you want to test. The calculator returns the gain, worked out as minus Rf divided by Rin, alongside the gain magnitude and the resulting output voltage for the input you specified. The minus sign matters: it shows the output is inverted, swinging in the opposite direction to the input, so a positive input voltage produces a negative output and vice versa. Because the gain depends purely on the ratio of the two resistors, you can quickly see how changing either value alters the amplification, whether you are designing a circuit from scratch or checking an existing one. Use it to size resistors for a target gain, to predict the output voltage a given input will produce, or to understand why a circuit behaves the way it does on the bench. The calculation assumes an ideal operational amplifier with enough open-loop gain that only the resistors set the closed-loop gain, so treat the result as a design estimate rather than an exact prediction, since real components, supply rails and bandwidth limits will affect the actual output.

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