Op-Amp Gain Calculator
Calculate inverting and non-inverting op-amp gain from the feedback and input resistors, in V/V and dB, plus the output voltage.
Op-amp gain
With negative feedback, an ideal op-amp's closed-loop gain is set only by the two resistors — not the op-amp itself. The two classic configurations give different gains and input behaviour.
Inverting: A_v = −R_f / R_in
Non-inverting: A_v = 1 + R_f / R_in
The inverting amp flips the signal's polarity (hence the minus sign) and its gain can be below 1; the non-inverting amp keeps polarity and its gain is always at least 1. Gain in decibels is 20·log₁₀|A_v|.
Worked example: a gain-of-10 stage
With R_in = 10 kΩ and R_f = 100 kΩ, the ratio R_f/R_in is 10. Wired as an inverting amplifier the gain is −10 V/V (20 dB); wired as non-inverting it is 1 + 10 = 11 V/V. A 0.1 V input therefore gives −1 V out of the inverting stage, or +1.1 V out of the non-inverting one.
Related
Set the resistor values with theresistor series & parallelcalculator, or convert a dB figure with thedecibel converter.
Common questions
- What is the difference between inverting and non-inverting gain?
- An inverting amplifier gives −Rf/Rin: the output is flipped in polarity, and the gain can be less than one. A non-inverting amplifier gives 1 + Rf/Rin: the output keeps its polarity, and the gain can never go below one, because of that leading 1. If you need attenuation without inversion, you need a divider before a buffer rather than a single stage.
- Why is the inverting gain negative?
- Because the signal enters at the inverting input, so a rising input drives a falling output. The minus sign is a phase inversion, not a mistake — a 1 V input with a gain of −10 gives −10 V. For AC signals it appears as a 180° phase shift, which matters when you cascade stages or feed a summing node, and is irrelevant if you only care about magnitude.
- What input impedance does each configuration have?
- This is the real reason to choose between them. The non-inverting configuration presents the op-amp's own input impedance, which is enormous — it barely loads the source at all. The inverting configuration presents Rin, because the inverting input sits at a virtual ground, so a 1 kΩ input resistor loads your source with 1 kΩ. For a high-impedance sensor, non-inverting is usually the only sensible choice.
- Can I get any gain I want by picking big resistors?
- Not in practice. Very large resistors make the circuit noisy and let the op-amp's input bias current produce meaningful offset voltages, while very small ones load the output. Roughly 1 kΩ to 100 kΩ is the comfortable range. There is also a bandwidth limit: an op-amp has a fixed gain-bandwidth product, so a gain of 100 on a 1 MHz part leaves you only 10 kHz of bandwidth.