Op-Amp Gain Calculator
Gain, output voltage and bandwidth for the standard op-amp configurations.
How it works
Two rules explain every op-amp circuit built with negative feedback: no current flows into the inputs, and the amplifier does whatever it takes at the output to hold the two inputs at the same voltage. Everything else is consequence.
Non-inverting: gain = 1 + Rf ÷ R1. The signal goes to the + input, so input impedance is enormous — hundreds of megohms — and the gain can never be less than 1.
Inverting: gain = −Rf ÷ R1. The − input sits at a virtual earth, so the input impedance is exactly R1 and no more. In exchange, the gain can be less than one, which the non-inverting configuration cannot do.
Voltage follower: gain of exactly 1, and it exists to convert a high-impedance source into a low-impedance one. It is the most-used op-amp circuit there is and it does nothing to the signal at all.
The limits are where real designs fail. Gain-bandwidth product is constant, so a 1 MHz part configured for a gain of 100 gives you 10 kHz of bandwidth, not 1 MHz — if the circuit sounds dull or the edges are soft, this is usually why.
Slew rate is a separate ceiling and catches people out because it depends on amplitude, not just frequency. A 0.5 V/µs part cannot produce a 10 V peak sine above about 8 kHz no matter what the bandwidth says, and what you get instead is a triangle wave.
And most op-amps do not swing to their rails. A classic bipolar part stops one and a half volts short at each end; rail-to-rail types get within tens of millivolts but only lightly loaded. On a single supply that means a mid-rail reference is not optional — without one, half the waveform is simply not available.
Common questions
Why is my high-gain circuit so slow?
Gain-bandwidth product is a constant for the part. Bandwidth is that product divided by your closed-loop gain, so a 1 MHz op-amp at a gain of 100 gives 10 kHz. Split it into two stages of gain 10 and you get 100 kHz.
Inverting or non-inverting?
Non-inverting when you need high input impedance and cannot load the source. Inverting when you need gain below 1, want the summing-junction property for mixing several inputs, or want the simpler single-supply biasing. The sign itself rarely matters.
What is slew rate limiting?
The maximum rate the output can change, independent of bandwidth. A large signal at high frequency demands a fast rate of change, and if the part cannot deliver it the sine turns into a triangle. Full-power bandwidth is slew rate divided by 2π times peak amplitude.
Can I run it from a single supply?
Yes, but the input and output must be biased to mid-rail, because the op-amp cannot produce a voltage outside its supplies. Without a mid-rail reference the negative half of any AC signal simply clips off at zero.