Op-Amp Gain Calculator (Inverting & Non-Inverting)

Op-amp gain: inverting and non-inverting

Both configurations assume an ideal op-amp in negative feedback: infinite open-loop gain, zero input bias current, and — because of the feedback — the two inputs sit at (almost) the same voltage. In the inverting config that shared voltage is 0 V (ground), a "virtual ground" at the − input, since + is tied to ground directly. Current through R1 has nowhere to go but through R2 (no current flows into the op-amp input), which gives A_v = −R2/R1 — gain and sign flip, input impedance ≈ R1.

In the non-inverting config, V_in drives the + input directly, and feedback forces the − input to the same voltage through the R1/R2 divider to ground. Solving that divider for the loop gain gives A_v = 1 + R2/R1 — always ≥ 1, no sign flip, and input impedance is very high (the op-amp's input impedance, not set by R1/R2). Setting R2 = 0 (or R1 = ∞) makes a unity-gain buffer.

Real op-amps deviate from these ideal formulas at high frequency (gain-bandwidth product limits) and with large output swings (slew rate) — treat this as the DC/low-frequency design starting point.