Op-Amp Gain Calculator
Choose the configuration, enter the resistors and signal to get gain, swing, bandwidth and slew limits.
Step-by-step
- Enter valid values to begin.
Model: ideal op-amp with a single-pole response, so closed-loop bandwidth = GBW / noise gain; for the differential amplifier the signal gain is Rf/R1 and noise gain 1 + Rf/R1. Single-supply mode assumes the signal is biased at half the supply, so the output swings ±(V/2 − headroom). GBW and slew-rate presets are typical datasheet values and vary part to part and with supply and load; verify for the exact part (a 741-class device is about 1 MHz and 0.5 V/µs). The differential CMRR estimate is the usual worst-case (1 + Rf/R1) / (4 × tolerance) for matched-ratio resistors and does not include the op-amp’s own CMRR. Bias-current error shown is Ib × Rf without compensation resistor.
Op-Amp Gain: Resistor Ratios, Noise Gain and What Limits Bandwidth
Core Engineering Principles
With negative feedback an op-amp makes its two inputs equal, and the resistor network sets how much of the output is fed back. That gives us three simple results: the inverting stage has gain −Rf/Rin and presents Rin to the source; the non-inverting stage has gain 1 + Rf/Rg and a very high input impedance; and the differential stage amplifies the difference with gain Rf/R1, provided the R3/R2 ratio matches Rf/R1. Resistor matching matters: with 1% resistors, the common-mode rejection of a gain-of-10 stage is only about 49 dB however good the op-amp is.
Gain isn’t free, though. The open-loop gain falls at 20 dB per decade, so the closed-loop bandwidth is the gain-bandwidth product divided by the noise gain, which is 1 + Rf/Rg in every configuration, even the inverting one. A second limit is slew rate: a large output swing at high frequency is limited to SR/(2π Vpk), whatever the small-signal bandwidth says. The output also stops 1.5 to 2 V short of the rails unless the part is rail-to-rail. We check clipping, bandwidth and slew limit together.
BW = GBW / (1 + Rf/Rg) • fFPBW = SR / (2π Vpk) • dB = 20 log10|Av|
NEC & Standard References
Manufacturer datasheets define gain-bandwidth product, slew rate, bias current and output swing, and the typical values in the presets here (LM358 near 1 MHz, TL072 near 3 MHz, OPA2134 near 8 MHz, NE5532 near 10 MHz) come from them and vary with the part and the supplier. IEC 60063 supplies the E-series values for the resistors, and tolerance classes come from the resistor’s own specification.1. Av = 1 + 10 / 1 = 11 V/V, which is 20.83 dB.
2. Vout = 11 × 0.5 = 5.5 V peak against a 10.5 V limit, so no clipping.
3. BW = 1 MHz / 11 = 90.9 kHz; the gain error at 5 kHz is 0.15%.
4. fFPBW = 0.5 V/µs / (2π × 5.5 V) = 14.5 kHz, above the 5 kHz signal.
5. Bias error ≈ 80 nA × 10 kΩ = 0.8 mV at the output.
- Slew limiting looks like distortion. A sine wave that turns triangular is slew-limited; reduce amplitude or choose a faster op-amp.
- Single-supply needs a bias. Without a mid-supply reference, an AC signal clips on its negative half-cycle.
- Check input range. Many op-amps misbehave if the inputs approach the rails; the non-inverting input range is not the same as the output swing.
- Resistor tolerance sets CMRR. A differential stage is only as good as its resistor matching; use thin-film networks for precision.