Op-Amp Gain Calculator
Inverting, non-inverting, and differential gain
Required Parameters
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Quick Answer
Non-inverting gain: G = 1 + Rf/Rg. Inverting gain: G = -Rf/Rin. Differential gain: G = Rf/R1 (when matched).
Design Notes
Op-amp gain is set by external resistors, not the op-amp itself. The Gain-Bandwidth Product (GBW) limits useful gain at high frequencies: at 10× gain with a 10 MHz GBW op-amp, bandwidth drops to 1 MHz. Use 1% or better resistors for precision gain stages. For gains >100, consider two cascaded stages to avoid bandwidth and stability issues.
Common Mistakes
- 1
Forgetting the sign inversion in inverting configurations — the output is 180° out of phase with the input.
- 2
Exceeding the GBW product — requesting too much gain at too high a frequency causes signal attenuation.
- 3
Not providing a DC bias path for the non-inverting input in AC-coupled designs.
Knowledge Base
What is the gain formula for a non-inverting op-amp?
Gain = 1 + Rf/Rg, where Rf is the feedback resistor and Rg is the ground resistor. The minimum gain is 1 (unity gain buffer, when Rf = 0). For example, Rf = 100kΩ, Rg = 10kΩ: Gain = 1 + 100k/10k = 11 (20.8 dB). The '+1' comes from the direct input path.
What is the gain formula for an inverting op-amp?
Gain = -Rf/Rin, where Rf is the feedback resistor and Rin is the input resistor. The negative sign indicates 180° phase inversion. Input impedance equals Rin. For Rf = 47kΩ, Rin = 10kΩ: Gain = -4.7 (output is inverted and 4.7× larger). Unlike non-inverting, gain can be less than 1 (attenuator).
What is gain-bandwidth product (GBW)?
GBW is constant for a given op-amp: GBW = Gain × Bandwidth. An op-amp with GBW = 10 MHz at gain 10 has 1 MHz bandwidth. At gain 100, bandwidth drops to 100 kHz. This is the fundamental speed-vs-gain tradeoff. Choose an op-amp with GBW ≥ 10× your required gain × bandwidth.
How do I build a differential amplifier?
Use four matched resistors: R1 from V1 to inverting input, Rf from inverting input to output, R2 from V2 to non-inverting input, Rg from non-inverting input to ground. When R1=R2 and Rf=Rg: Vout = (Rf/R1)(V2-V1). Match resistors to ≤0.1% for good common-mode rejection (CMRR).
What op-amp should I use for my project?
General purpose: LM358 (dual, cheap), TLV2372 (rail-to-rail). Precision: OPA2277 (low offset), AD8628 (auto-zero). High speed: OPA2356 (200MHz), AD8065 (145MHz). Low noise: OPA1612 (audio), ADA4896 (RF). Low power: MCP6001 (100µA), OPA379 (2.9µA). Always check: supply voltage range, input/output swing, GBW, slew rate, and input bias current.
Why is my op-amp output clipping or railing?
Common causes: (1) Output trying to exceed supply rails — use rail-to-rail output op-amps. (2) Input common-mode range violated. (3) Gain too high causing saturation from offset voltage. (4) No DC bias path for AC-coupled inputs. (5) Load impedance too low for the op-amp's output drive capability.