Op-Amp Gain Calculator
Inverting and non-inverting gain from Rf and Rg — with gain in dB and output voltage.
The two basic gain stages
With ideal negative feedback the closed-loop gain depends only on the resistor ratio:
The non-inverting amp keeps the input in phase and has very high input impedance (gain ≥ 1). The inverting amp flips the phase and its input impedance equals . Express either as decibels with
Real gain is limited by the op-amp's gain-bandwidth product, so a high gain shrinks your usable bandwidth — check the GBW before committing to large resistor ratios.
Frequently asked questions
How do I calculate non-inverting op-amp gain?
Gain = 1 + Rf/Rg, where Rf is the feedback resistor and Rg goes from the inverting input to ground. The output is in phase with the input and the minimum gain is 1 (a buffer when Rf = 0).
How do I calculate inverting op-amp gain?
Gain = −Rf/Rin, where Rin is the input resistor and Rf is the feedback resistor. The minus sign means the output is inverted (180° out of phase). The input impedance equals Rin.
How do I convert gain to decibels?
Voltage gain in dB = 20 × log10(|A|). So a gain of 10 is 20 dB, a gain of 100 is 40 dB, and a unity buffer (gain 1) is 0 dB.
What resistor values should I pick?
Keep Rf and Rg in the kΩ–100 kΩ range: too low wastes current and loads the output, too high lets bias current and noise dominate. Set the ratio for your gain, then round both to standard E-series values.