Inverting Op-Amp Gain Calculator

About this calculator

An inverting op-amp circuit feeds the output back to the inverting (−) input through a resistor Rf, while the signal enters through another resistor Rin and the non-inverting input is grounded. Because the op-amp’s open-loop gain is enormous, negative feedback forces the inverting input to sit at a “virtual ground” — the same 0 V as the non-inverting pin — even though no current actually flows into that pin. All the input current through Rin is forced through Rf instead, which gives the closed-loop gain Av = −Rf/Rin, with the minus sign meaning the output is 180° out of phase with the input.

This topology is one of the most common building blocks in analog electronics: audio mixers, active filters, current-to-voltage converters, and signal-conditioning front ends all use it because the gain depends only on a resistor ratio, not on the op-amp’s own (variable) open-loop gain. The output voltage is simply Vout = −(Rf/Rin) · Vin, clamped in practice by the supply rails — this calculator applies that formula directly from the resistor values and input voltage you enter.