Op-Amp Gain Calculator

Created: 19/03/2026Updated: 13/06/2026By: Mert
Op-Amp Gain Calculator
Inv: −Rf/Rin
Non-Inv: 1+Rf/Rin
Diff: Rf/Rin
Op-Amp Gain Calculator
Rf Feedback Resistor (Ω)
Rin Input Resistor (Ω)
Configuration
Enter values
Op-Amp Gain Calculator Results
Gain Av
—
×
Gain (dB)
—
dB
Phase
—
°
Rf/Rin Ratio
—
×
Input Impedance
—
Ω
Formula
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Op-Amp Gain Calculator Input Output

Figure 1: Op-Amp Gain Calculator — enter values to calculate the result with step-by-step workings.

Table of Contents
Fundamentals
  1. How Op-Amp Gain Works
  2. The Three Configurations
Worked Examples
  1. Inverting ×−10
  2. Non-Inverting ×11
  3. Unity Gain Buffer
Deep Dive
  1. Gain-Bandwidth Product
  2. Rail-to-Rail and Saturation
Reference
  1. Frequently Asked Questions
  2. Related Calculators

How Op-Amp Gain Works

An op-amp is a high-gain differential amplifier. With negative feedback (a resistor from output to inverting input), the gain becomes set entirely by external resistor ratios — independent of the op-amp’s internal gain. This is why op-amp circuits are predictable, stable, and easy to design. The calculator above computes gain, dB, phase, and input impedance for inverting, non-inverting, and differential configurations.

The Transistor Biasing Calculator designs discrete amplifiers where gain depends on transistor parameters. Op-amps eliminate that dependency through feedback, trading simplicity for the cost of a dedicated IC.

The Three Configurations

Inverting: Av = −Rf/Rin, phase = 180°, Zin = Rin
Non-inverting: Av = 1 + Rf/Rin, phase = 0°, Zin = very high
Differential: Av = Rf/Rin, phase = 0°, Zin = Rin

Example: Inverting ×−10

Rf = 10 kΩ, Rin = 1 kΩ, Inverting

Av = −10k/1k = −10

dB = 20 log(10) = 20 dB

Phase = 180° (output inverted)

Zin = 1 kΩ (virtual ground at inverting input)

A 100 mV input produces a −1 V output. The BJT Gain Calculator shows that achieving 20 dB voltage gain with a discrete BJT requires careful biasing and RC/RE selection.

Example: Non-Inverting ×11

Rf = 10 kΩ, Rin = 1 kΩ, Non-Inverting

Av = 1 + 10k/1k = 11

Zin = Very high (op-amp input impedance, typically >1 MΩ)

Non-inverting has higher input impedance — use it for high-impedance sources (sensors, piezo pickups). The Emitter Resistor Calculator shows how discrete amplifiers with RE unbypassed also achieve predictable (but lower) gain from a resistor ratio.

Example: Unity Gain Buffer

Rf = 0 (short), Rin = open, Non-Inverting

Av = 1 (output follows input exactly)

Used to isolate a high-impedance source from a low-impedance load. The op-amp provides current gain without voltage gain. The MOSFET Gate Resistor Calculator can design the gate drive for a MOSFET buffer that serves a similar isolation purpose at higher power levels.

Gain-Bandwidth Product

Every op-amp has a gain-bandwidth product (GBW): gain × bandwidth = constant. A 1 MHz GBW op-amp at gain = 10 has only 100 kHz bandwidth. At gain = 100, only 10 kHz. For wideband amplifiers, choose an op-amp with GBW well above your required gain × bandwidth. The 555 Timer Calculator generates square waves up to 500 kHz without the bandwidth limitations of linear amplifiers.

Rail-to-Rail and Saturation

Standard op-amps cannot swing their output to the supply rails — they saturate 1–2 V below V+ and above V−. Rail-to-rail op-amps swing within 50–200 mV of the rails. For single-supply circuits (V+ = 5V, V− = 0V), rail-to-rail output is essential to use the full voltage range. The LM317 Resistor Calculator handles a related output voltage limitation where the regulator needs 2–3 V of headroom.

Frequently Asked Questions

What is the difference between inverting and non-inverting?
Inverting: gain = −Rf/Rin, 180° phase shift, Zin = Rin. Non-inverting: gain = 1+Rf/Rin, 0° phase, very high Zin. Use non-inverting for high-impedance sources.
What is a unity gain buffer?
Rf = 0 (short), no Rin. Gain = 1. Output follows input. Provides current amplification and impedance isolation without voltage gain.
What limits the gain?
The gain-bandwidth product. At high gain, bandwidth drops: BW = GBW/gain. A 1 MHz GBW op-amp gives only 10 kHz at gain = 100. The MOSFET Calculator shows gm-based gain in discrete FET amplifiers that can achieve wider bandwidth.
What about rail-to-rail output?
Standard op-amps saturate 1–2 V from the rails. Rail-to-rail types swing within 50–200 mV. Essential for single-supply and low-voltage circuits. The MOSFET Threshold Voltage Calculator addresses a related voltage headroom concern.
How do I choose Rf and Rin?
The ratio sets the gain. Absolute values affect noise and bandwidth. Rin = 1–10 kΩ is a good starting range. Lower = less noise but more current. Higher = less current but more thermal noise. The Shockley Diode Calculator models junction noise at the fundamental level. The Transistor Base Resistor Calculator uses a similar Ohm’s law approach to find a single resistor value from voltage and current requirements.

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Last updated: March 2026