About the Op-Amp Gain Calculator
This calculator finds the voltage gain of an operational amplifier circuit built in either the inverting or non-inverting configuration, based on the feedback and input resistor values you specify. It also projects the output voltage for a given input voltage at that gain, which is useful for confirming a resistor pair will produce the amplification and output range you're aiming for before building the circuit.
How It Works
You select which configuration you're working with, non-inverting or inverting, then enter the feedback resistor (Rf), the input resistor (Rin), and an input voltage. The calculator applies the gain formula that matches your selected configuration, then multiplies that gain by the input voltage to estimate the resulting output voltage. Because both formulas divide by the input resistor, an Rin value of zero returns an error instead of a result.
Examples
Non-inverting amplifier
Rf = 10,000 ohms and Rin = 1,000 ohms in the non-inverting configuration gives a gain of 1 + (10000 / 1000) = 11x. A 1V input produces an estimated 11V output.
Inverting amplifier
The same resistor values in the inverting configuration give a gain of -(10000 / 1000) = -10x. A 1V input produces an estimated -10V output, an inverted and amplified version of the input signal.
Advantages
- Covers both standard op-amp topologies in one tool, avoiding the need to look up two separate formulas depending on the circuit type.
- Reports the projected output voltage alongside the gain, helping catch resistor combinations that would push the output beyond a realistic range.
- Removes the manual arithmetic of resistor ratios, which is easy to get wrong when comparing several candidate resistor pairs.
Common Mistakes
- Selecting the wrong configuration for the circuit actually being built, since the non-inverting formula includes an extra +1 term that the inverting formula does not.
- Misreading a negative inverting gain as weaker amplification than a positive number of the same magnitude, when the sign only indicates phase inversion, not strength.
- Not checking whether the projected output voltage would exceed the op-amp's real supply voltage, which would cause clipping in an actual circuit.
Edge Cases to Watch For
- An input resistor (Rin) of zero returns an error, since both gain formulas divide by that value.
- Non-inverting gain can never drop below 1 for positive resistor values, since it's always 1 plus a positive fraction, while inverting gain has no such floor and can reach any negative magnitude depending on the resistor ratio.
- The output voltage figure assumes an ideal, unsaturated op-amp and doesn't account for the amplifier's actual supply rail limits, so a real circuit would clip before reaching a very large calculated output.
Common Use Cases
- Electronics students and hobbyists designing an amplifier stage and comparing resistor ratios before building it on a breadboard.
- Engineers verifying that resistor values in an existing schematic or datasheet reference design actually deliver the intended gain.
- Anyone converting a target amplification factor into an initial pair of resistor values for further refinement.