Free Op-Amp Gain Calculator Online — Big Das

Op-Amp Gain Calculator

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Design inverting and non-inverting op-amp circuits in seconds.

Free Op-Amp Gain Calculator Online — Big Das

The operational amplifier is the workhorse of analog electronics. Whether you are building an audio preamp, a sensor signal conditioner, or an active filter, the very first design decision is always the same: *how much gain do I need, and which resistors get me there?

• Our free Op-Amp Gain Calculator answers both questions instantly — and tells you the bandwidth your gain actually costs you.

What Is an Op-Amp Gain Calculator?

An op-amp gain calculator computes the relationship between resistor values and closed-loop gain for the two classic amplifier topologies:

• Inverting amplifier — the input signal is applied through Rin to the inverting (−) input; the output is inverted.
• Non-inverting amplifier — the input drives the non-inverting (+) input directly; the output keeps its polarity.

Because the op-amp's open-loop gain is enormous (typically 100 dB or more), the final closed-loop gain is set almost entirely by the two external resistors — not by the chip itself. That makes the math simple, predictable, and exactly the kind of thing a calculator should do for you.

How to Use the Tool

1. Choose the configuration — Inverting or Non-Inverting.
2. Enter Rf and Rin/R1 with their units (Ω, kΩ, or MΩ). The gain updates live.
3. Solve a resistor for a target gain — enter your desired gain and one known resistor; the tool computes the missing value.
4. Enter the op-amp's Gain-Bandwidth Product (GBW) from its datasheet to see the resulting −3dB cutoff frequency.

The Formulas

• Inverting gain: A = −Rf / Rin
• Non-inverting gain: A = 1 + Rf / R1
• Solve Rf for a target non-inverting gain G: Rf = R1 × (G − 1)
• Solve R1: R1 = Rf / (G − 1) — for inverting, simply Rin = Rf / G.
• −3dB cutoff frequency: fc = GBW / (1 + Rf / Rin)

Note the last formula carefully: the bandwidth depends on the noise gain (1 + Rf/Rin), not the signal gain. This is why an inverting amplifier of gain −10 and a non-inverting amplifier of gain +11 have the same bandwidth.

Worked Example

You need an inverting preamp with a gain of −10 using an op-amp rated at 1 MHz GBW. Pick Rf = 100 kΩ, so Rin = Rf / G = 100 kΩ / 10 = 10 kΩ. The calculator shows:

• Gain: −10 V/V (20 dB)

• Noise gain: 1 + 100/10 = 11

• −3dB cutoff: 1 MHz / 11 ≈ *90.9 kHz

Had you built the same circuit non-inverting, the gain would be +11, not +10 — a classic trap for beginners, and a good reason to double-check with a calculator before soldering.

Common Use Cases

• Audio design: microphone preamps, mixers, tone-control stages, and guitar pedals.
• Sensor interfaces: amplifying millivolt-level signals from thermocouples, strain gauges, and photodiodes before an ADC.
• Active filters: setting passband gain in Sallen-Key and multiple-feedback topologies.
• Education: verifying lab exercises and homework calculations in analog electronics courses.

Frequently Asked Questions

Can the non-inverting amplifier have a gain less than 1?

No. The formula 1 + Rf/R1 has a minimum of 1 (unity gain), reached when Rf is zero or R1 is open. For attenuation you need an inverting stage or a passive divider. The tool flags this case automatically.

Why does higher gain reduce bandwidth?

The op-amp's gain-bandwidth product is constant. Closing the loop with a higher feedback factor forces the closed-loop gain down, and the frequency where loop gain runs out moves down with it: fc = GBW / noise gain.

Is the −3dB cutoff the same for inverting and non-inverting?

Only at the same noise gain. The noise gain is 1 + Rf/Rin for both topologies, so an inverting gain of −9 and a non-inverting gain of +10 share the same bandwidth.

What resistor values are practical?

Typical designs keep Rf between about 1 kΩ and 1 MΩ. Very small resistors load the output stage; very large ones add Johnson noise and make the circuit sensitive to bias currents and PCB leakage.

Does this work for single-supply circuits?

Yes — the gain formulas are unchanged. Single-supply operation only adds a biasing network (usually a Vcc/2 reference) that doesn't enter the AC gain calculation.

What about input and output impedance?

An inverting amplifier's input impedance equals Rin, while the non-inverting input impedance is very high (the op-amp's own input impedance). Both have very low output impedance within the passband.