Op-Amp Gain Calculator
Use this tool to calculate closed-loop voltage gain, output voltage, and solve for missing resistor values for inverting and non-inverting op-amp circuits.
Non-inverting: Av = 1 + (Rf / Rg)
Inverting: Av = - (Rf / Rin)
Output voltage: Vout = Av × Vin
What Is a Gain Op Amp Calculator?
A gain op amp calculator helps you quickly determine how much an operational amplifier circuit will scale an input signal. In analog design, this is one of the most common calculations: you know the resistor values, and you need gain. Or, you know the gain you want, and you need resistor values that produce it.
Instead of manually repeating equations every time, a calculator reduces errors and speeds up circuit planning. It is especially useful during early design, prototyping, and troubleshooting.
Two Core Amplifier Configurations
1) Non-inverting amplifier
In this configuration, the input signal goes to the non-inverting terminal (+). The output remains in phase with the input, and the gain equation is:
Av = 1 + (Rf / Rg)
- Rf: feedback resistor from output to inverting input
- Rg: resistor from inverting input to ground
Important behavior: the smallest gain you can get is 1 (a voltage follower). You cannot get gain below 1 with this basic topology.
2) Inverting amplifier
In this configuration, the input signal is applied through an input resistor to the inverting terminal (−). The output is 180° out of phase with the input:
Av = - (Rf / Rin)
- Rf: feedback resistor
- Rin: resistor between source and inverting input
The negative sign indicates phase inversion. For example, if gain is -10 and input is +0.2 V, output ideal is -2 V (subject to power rails and op-amp limits).
How to Use the Calculator
- Select non-inverting or inverting.
- Enter resistor values in ohms.
- Enter input voltage if you want output voltage prediction.
- Click Calculate Gain & Vout to compute gain, dB gain, and output voltage.
- Use Solve Rf or Solve Rg/Rin with a target gain to size one resistor from the other.
The calculator reports both linear gain and decibel gain:
Gain(dB) = 20 log10(|Av|)
Worked Examples
Example A: Non-inverting gain of 6
Suppose Rg = 10 kΩ and Rf = 50 kΩ.
Av = 1 + (50k / 10k) = 1 + 5 = 6
If Vin = 0.3 V, ideal Vout = 1.8 V.
Example B: Inverting gain of -12
Let Rin = 5 kΩ and Rf = 60 kΩ.
Av = - (60k / 5k) = -12
If Vin = 0.1 V, ideal Vout = -1.2 V.
Example C: Solve resistor from target gain
You want non-inverting Av = 11 and already chose Rg = 2 kΩ:
Rf = (Av - 1) × Rg = (11 - 1) × 2k = 20 kΩ.
Practical Design Tips
Use reasonable resistor ranges
Very low resistor values increase current draw. Very high values can increase noise and bias-current-induced errors. A common practical range is around 1 kΩ to 100 kΩ, often centered near 10 kΩ to 47 kΩ.
Check output swing limits
Your computed output is ideal. Real op-amps cannot swing beyond their supply rails. If you power an op-amp at ±5 V, a requested output of ±6 V will clip.
Watch bandwidth and stability
Closed-loop gain affects bandwidth. For many op-amps, increasing gain reduces available bandwidth. Also verify phase margin, compensation, and load conditions to avoid oscillation.
Include tolerance in your design
Real resistors have tolerance (1%, 0.1%, etc.). Gain will vary with those tolerances. For precision applications, use matched, low-drift resistors.
Common Mistakes to Avoid
- Mixing up inverting and non-inverting equations.
- Forgetting the negative sign in inverting gain.
- Using kΩ in one place and Ω in another by accident.
- Ignoring power-supply headroom and output clipping.
- Assuming ideal behavior at very high frequency.
Quick FAQ
Can non-inverting gain be less than 1?
Not in the simple standard non-inverting circuit. Minimum is 1.
Why is my measured gain different from calculated gain?
Likely reasons include resistor tolerance, source/load interaction, op-amp finite open-loop gain, bandwidth limits, and measurement setup effects.
Should I always pick exact calculated resistor values?
Not necessarily. Choose nearest standard values (E24/E96), then recalculate expected gain and verify it meets your requirement.
Final Note
This gain op amp calculator is a fast starting point for analog design. It handles the core math instantly, but final circuits should always be checked against real op-amp datasheet limits, temperature behavior, noise goals, and stability requirements.