Op-Amp Gain Calculator
Calculates gain (in V/V and dB) and output voltage for five basic op-amp circuit configurations: non-inverting, inverting, differential, voltage follower, and non-inverting summing amplifier.
FreeOnline Tool
Loading…
How to Use
- Select a circuit type at the top: non-inverting, inverting, differential, voltage follower, or summing amplifier — the input fields below update automatically.
- Toggle between Ω and kΩ resistor input units using the unit switch; all resistor fields rescale accordingly.
- Fill in the parameters for your selected circuit:
· Non-inverting/Inverting: input voltage Vin, feedback resistor Rf, ground resistor Rg;
· Differential: inverting-input voltage V1, non-inverting-input voltage V2, feedback resistor Rf, ground resistor Rg (assumes R1=Rg and R2=Rf are matched);
· Voltage follower: input voltage Vin only;
· Summing amplifier: up to three input voltage/resistor pairs (V1/R1, V2/R2, V3/R3) plus feedback resistor Rf and ground resistor Rg. - Gain (in both V/V and dB) and output voltage Vout are computed and displayed in real time, along with a formula description for the selected circuit.
- If Rf or Rg is entered as 0 or negative, an error message ("Rf and Rg must be positive") appears instead of a result.
- Click "Load Sample Data" to reset to the default non-inverting amplifier example.
Features
- Supports gain calculation for five fundamental op-amp circuits: non-inverting (Gain=1+Rf/Rg), inverting (Gain=-Rf/Rg), differential (Vout=(V2-V1)×Rf/Rg), voltage follower (Gain=1), and non-inverting summing amplifier (weighted sum of multiple inputs, then amplified).
- Gain results are shown in both V/V (voltage ratio) and dB (20×log10|Gain|) units.
- Ω/kΩ resistor unit toggle lets you enter common resistor values (e.g., 10kΩ) directly without manual conversion to ohms.
- The summing amplifier supports up to three independent input voltage/resistor pairs, automatically computing the parallel resistance and the weighted-sum output voltage.
- Validates edge cases such as non-positive feedback/ground resistors or a summing amplifier with no valid input channels, returning clear error text instead of a meaningless result.
- Every calculation generates a text description of the circuit with the actual substituted values, useful for design documentation and review.
Use Cases
Sensor signal conditioning gain design
Design a non-inverting or inverting amplifier stage for weak sensor outputs (temperature, pressure, etc.), working backward from the ADC's full-scale range to find the needed Rf/Rg ratio.
Differential amplifier design for current-sense circuits
Design a differential amplifier for current-sense shunt resistors or differential sensor outputs, computing the actual output voltage and gain for a given Rf/Rg pair.
Voltage follower impedance-buffer verification
Confirm that a voltage-follower stage (Gain=1) outputs a voltage equal to the input, useful for quickly checking impedance-matching or buffer-stage designs.
Multi-channel summing amplifier design
When designing an audio mixing circuit or a multi-sensor signal-combining stage, use the summing amplifier mode to compute the mixed output voltage under different weighting (different input resistors).
FAQ
How is the dB gain value calculated?
The tool uses the standard voltage-gain-to-decibel formula dB = 20 × log10(|Gain|), taking the absolute value of the gain (an inverting amplifier's V/V gain is negative, but dB only reflects magnitude, not phase inversion).
Why is the inverting amplifier's V/V gain negative?
This reflects the inherent behavior of an inverting amplifier: the output is 180° out of phase with the input. The gain formula Gain=-Rf/Rg carries the negative sign to indicate phase inversion. When |Rf/Rg|<1, the circuit actually attenuates rather than amplifies — the gain magnitude is below 1 but still a valid result.
Why isn't there a separate input for R1/R2 in the differential amplifier?
A standard differential amplifier requires R1=Rg (the resistor at the inverting input) and R2=Rf (the resistor at the non-inverting input) to be strictly matched to preserve common-mode rejection. The tool simplifies this by requiring only Rf and Rg, using Vout=(V2-V1)×(Rf/Rg). If your actual circuit has R1≠Rg or R2≠Rf, this tool's result won't directly apply.
Can I leave the third input channel empty in the summing amplifier?
Yes. In summing mode, each channel is only counted if it has both a valid voltage and a resistance greater than 0; any channel left empty or with a resistance of 0/negative is automatically ignored without causing an error. As long as at least one channel has valid input, a result is produced.