About the Op-Amp Gain Calculator
This op-amp gain calculator gives the closed-loop voltage gain of the four most common operational-amplifier circuits — inverting, non-inverting, unity-gain voltage follower and the classic four-resistor difference (differential) amplifier — from the feedback and input resistor values. It shows the gain as a ratio and in decibels, the ideal output voltage for your input, and the output you will actually get once the op-amp hits its supply rails.
It is meant for hobbyists building preamps and sensor interfaces, students learning feedback circuits, and engineers doing a quick sanity check before simulation. The transfer chart plots output against input so you can see exactly where the amplifier starts to clip.
Results assume an ideal op-amp: infinite open-loop gain, no input current and no offset. Real parts limit gain at high frequencies (gain-bandwidth product) and most cannot swing all the way to the rails, so enter the output headroom from your op-amp’s datasheet (about 1.5 V for classic parts like the 741 or TL072, near 0 V for rail-to-rail types). The difference amplifier assumes matched resistor pairs (R3 = Rin, R4 = Rf).
With the default inputs, the voltage gain is -10 V/V. Change any value above to recalculate instantly.
How to use the op-amp gain calculator
- 1Pick the amplifier configuration.
- 2Enter Rf and Rin in kilohms (not needed for a voltage follower).
- 3Enter the input voltage (and V2 for a difference amplifier).
- 4Enter the supply rails and your op-amp’s output headroom.
- 5Read the gain, dB value and output, and check the chart for clipping.
Formula and method
With negative feedback an ideal op-amp drives its output until both inputs sit at the same voltage. In the inverting circuit the − input is a virtual ground, so the input current Vin/Rin must flow through Rf, giving Vout = −(Rf/Rin)·Vin. In the non-inverting circuit Rf and Rin form a divider that feeds back a fraction of the output, so Vout = (1 + Rf/Rin)·Vin; with no divider (follower) the gain is exactly 1.
The four-resistor difference amplifier with matched pairs (R1 = R3 = Rin, R2 = R4 = Rf) amplifies only the difference between its inputs: Vout = (Rf/Rin)(V2 − V1). Voltage gain in decibels is 20·log10 of its magnitude. Finally the output is limited to the supply rails minus the headroom the op-amp needs, which is where clipping begins.
- G
- Closed-loop voltage gain (V/V)
- Rf
- Feedback resistor (output to − input)
- Rin
- Input resistor (inverting) or ground leg (non-inverting)
- V1, V2
- Inputs of the difference amplifier (− and + side)
- Vout
- Output voltage
Worked examples
Inverting amp, Rf 100 kΩ, Rin 10 kΩ, 0.5 V in
G = −100/10 = −10 (20 dB), so 0.5 V in gives −5 V out. With ±15 V rails and 1.5 V headroom the output can swing ±13.5 V, so any input up to 1.35 V is amplified cleanly.
Non-inverting amp that clips
G = 1 + 47/4.7 = 11 (20.83 dB). 2 V × 11 = 22 V, but with ±12 V rails and 1.5 V headroom the output saturates at 10.5 V. Inputs must stay below 10.5/11 ≈ 0.95 V.
Difference amp on a sensor bridge
With matched 100 kΩ/10 kΩ pairs the differential gain is 10. The inputs differ by 0.52 − 0.50 = 0.02 V, so the output is 0.2 V; the common 0.5 V is rejected.
Frequently asked questions
What is the gain of an inverting op-amp?+
G = −Rf/Rin. The minus sign means the output is inverted (180° out of phase). With Rf = 100 kΩ and Rin = 10 kΩ the gain is −10, or 20 dB.
What is the gain of a non-inverting op-amp?+
G = 1 + Rf/Rin, where Rin goes from the inverting input to ground. The gain can never be less than 1, and the output has the same polarity as the input.
How do I convert op-amp gain to dB?+
Voltage gain in dB is 20 × log10(|G|). A gain of 10 is 20 dB, 100 is 40 dB and 2 is about 6 dB. A gain below 1 gives a negative dB value.
Why is my op-amp output clipping?+
The output cannot exceed the supply rails, and most op-amps stop 1–2 V short of them. If gain × input is larger than that swing, the waveform flattens. Lower the gain, reduce the input or use higher rails or a rail-to-rail op-amp.
Does op-amp gain depend on frequency?+
Yes. Real op-amps have a gain-bandwidth product (GBW): for a 1 MHz GBW part set to a noise gain of 10, the gain starts falling at about 100 kHz. This calculator gives the low-frequency, ideal gain.