Electrical & Electronics
Op-Amp Gain & Feedback Calculator
Calculate inverting or non-inverting op-amp gain and output, or find standard feedback resistor pairs for a target gain.
Your inputs
Your results
- Voltage gain
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- Ideal output voltage
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- Bounded output estimate
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- Feedback resistor
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G = 1 + Rf / RgBest resistor pairs
| Rg | Rf | Voltage gain | Target error · % | Use pair |
|---|
Set op-amp gain and compare feedback resistor pairs
Calculate ideal closed-loop gain and output voltage for an inverting or non-inverting amplifier. Include a reference voltage, compare preferred feedback resistors and optionally bound the output with limits you supply. The tool models an ideal amplifier and static output limiting; it does not calculate bandwidth, slew rate, input-range restrictions or load-dependent output swing.
Step by step
- Choose the amplifier topology and calculation mode. Enter input voltage and reference voltage, then Rin or Rg and feedback resistance Rf. The resistance fields default to kΩ.
- Optionally enable output limits and enter the actual lower and upper output bounds you want to model. Compare ideal output with limited output and check whether the status indicates clipping.
- To compare resistor pairs, choose search mode, enter the target gain magnitude, resistance scale and preferred series. Review the listed gain errors; use a pair to return to calculation mode and inspect its output.
Settings and limits
- Gain and reference
- Inverting gain is G = −Rf / Rin; non-inverting gain is G = 1 + Rf / Rg. Output is Vout = Vref + G × (Vin − Vref). Reference is connected to the non-inverting input for the inverting circuit, or to the lower end of Rg for the non-inverting circuit.
- Output limits
- The lower bound must be below the upper bound. The model clamps ideal output to those entered values; it does not derive them from supply rails. Actual output swing depends on the chosen amplifier and operating conditions, so use appropriate bounds from its specifications.
- Resistor search
- Search uses a positive gain magnitude even for an inverting amplifier; the listed inverting gain is negative. Non-inverting target gain must be at least 1. The bounded search lists up to five preferred-value pairs and reports relative gain error; it does not account for resistor tolerance or amplifier errors.
Worked example
Choose non-inverting calculation with Vin = 0.2 V, Vref = 0 V, Rg = 10 kΩ and Rf = 90 kΩ. Enable output limits of 0 V and 3.3 V. Gain is 10 V/V and output is 2 V.
| Vin | G | Vout* | Vout (0–3.3 V) |
|---|---|---|---|
| 0.2 V | 10 V/V | 2 V | 2 V |
| 0.4 V | 10 V/V | 4 V | 3.3 V |
Increase Vin to 0.4 V without changing the resistors. Ideal output becomes 4 V, but the limited result is 3.3 V and the status indicates clipping. The gain calculation is unchanged; the entered output ceiling prevents the modeled output from following the ideal value.
Questions and troubleshooting
Why is the inverting result negative?
With a zero reference, positive input produces negative ideal output through the negative gain. A single-supply circuit may not be able to reach that value. Set a suitable reference and realistic output limits before interpreting the result as an operating point.
Does a correct resistor ratio guarantee the expected signal?
The ratio defines this ideal static gain. Frequency response, input common-mode range, output loading, bias effects and stability need the actual amplifier's specifications. Use the separate bandwidth and slew-rate tool when exploring those signal-speed limits.
Why are search results or calculated values blank?
Check for a positive input resistor, a nonnegative feedback resistor, valid units and ordered output limits. Search also requires a valid gain magnitude and resistance scale. The input and reference voltages may be signed, but invalid resistance or target entries must be corrected.