What is the inverting amplifier gain formula?

For an inverting op-amp the closed-loop gain is −Rf/Rin, where Rf is the feedback resistor and Rin is the input resistor. Example: with Rf = 10 kΩ and Rin = 1 kΩ the gain is −10, meaning a 0.1 V input becomes a −1 V output. The minus sign is not an error, it tells you the output is 180 degrees out of phase with the input, the defining trait of the inverting topology.

What is the non-inverting amplifier gain formula?

For a non-inverting op-amp the gain is 1+Rf/Rin. The same Rf = 10 kΩ and Rin = 1 kΩ now give 1 + 10 = 11, so a 0.1 V input becomes +1.1 V with no phase flip. The extra plus one comes from the input feeding the non-inverting terminal directly, which is why a non-inverting stage can never have a gain below unity, the floor is exactly 1 when Rf is zero.

How do I convert the gain to decibels?

Voltage gain in decibels is 20·log10 of the magnitude of the gain. A gain of 10 is 20 dB, a gain of 100 is 40 dB, a gain of 2 is about 6.02 dB, and unity gain (1) is 0 dB. The magnitude is used, so the inverting gain of −10 is also 20 dB because the sign affects phase, not amplitude. The 20 in front is for amplitude ratios; power ratios would use 10 instead.

How is the output voltage computed?

Output voltage is gain multiplied by input voltage. With an inverting gain of −10 and a 0.1 V input you get −1 V; with a non-inverting gain of 11 and a 0.1 V input you get 1.1 V. Watch the supply rails: a real op-amp clips when the computed output exceeds the supply, so a 11× stage on a 5 V rail saturates once the input passes roughly 0.45 V. The tool reports the ideal value so you can spot clipping yourself.

How do I pick resistors for a target gain?

Reverse mode turns a wanted gain into an Rf to Rin ratio. For an inverting gain of −5 you need Rf/Rin = 5, so Rf = 50 kΩ with Rin = 10 kΩ works. For a non-inverting gain of 5 you need Rf/Rin = 4. Then snap to standard E24 values, keep Rin in the 1 kΩ to 100 kΩ band to balance noise against bias current error, and verify the realised gain back in forward mode.

Why does the inverting gain show a negative sign?

The negative sign is physical, not cosmetic. An inverting stage holds its summing junction at a virtual ground, so current pushed in through Rin must flow out through Rf, which pulls the output the opposite way to the input. A rising input produces a falling output, a 180 degree phase shift. For magnitude only, take the absolute value: a gain of −10 has a magnitude of 10 and a decibel value of 20 dB, identical to a non-inverting 10.

Match a measured dB headroom to a real resistor pair

Your audio buffer must add 12 dB without clipping the 3.3 V rail. Drop 12 dB into reverse mode, read a voltage gain near 4, and the tool hands you Rf/Rin = 3 for the non-inverting build. Pick Rf = 30k, Rin = 10k, then jump to forward mode to confirm a 0.6 V peak input stays under the rail.

Spot clipping before you breadboard

You set Rf = 47k, Rin = 1k and enter a 0.2 V input. The tool reports an inverting gain of -47 and an ideal output of -9.4 V. On a plus-minus 5 V supply that number screams saturation, so you raise Rin to 10k for a -4.7 gain and a clean -0.94 V before soldering anything.

Op-Amp Gain Calculator — Inverting and Non-Inverting

Inverting −Rf/Rin and non-inverting 1+Rf/Rin gain, in V/V and dB, with output voltage and a reverse resistor solver, browser-only

Runs locally
Category Calculator
Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.

Enter the feedback resistor Rf and input resistor Rin. The closed-loop gain is shown as a multiplier, in dB, and as an output voltage.

Topology

Mode

Feedback resistor Rf (kΩ)Input resistor Rin (kΩ)Input voltage Vin (V)

Gain

-10 V/V

180° phase flip

Gain in dB

20 dB

Output voltage Vout

-1 V

Formula

gain = −Rf / Rin

What this tool does

A focused operational amplifier gain calculator for inverting and non-inverting op-amp stages. Type the feedback resistor Rf and the input resistor Rin and read the closed-loop gain three ways at once: as a plain multiplier (V/V), as a decibel figure using 20·log10 of the magnitude, and as an output voltage for whatever input swing you enter. The inverting topology returns −Rf/Rin, so the sign tells you the output is phase flipped 180 degrees; the non-inverting topology returns 1+Rf/Rin and never drops below unity. Flip into reverse mode to go the other way: name a target gain and the tool hands back the Rf to Rin ratio you need, so you can pick standard E12 or E24 resistor values instead of guessing. Every result copies to the clipboard with one click, and the shareable link reopens the exact configuration. All math is plain JavaScript that runs in the browser tab. Nothing is uploaded, nothing is logged.

Tool details

Input: Numbers; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: Shareable URL state; Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget: Initial JS <= 9 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Calculator · Developer; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

How Op-Amp Gain Calculator fits into your work

Use it for fast estimates, comparisons, and planning numbers before you make the final call.

Calculation jobs

Getting a realistic range before a purchase, plan, workout, or schedule decision.
Comparing scenarios by changing one input at a time.
Turning rough assumptions into a number you can discuss.

Calculation checks

Double-check units, dates, rates, and rounding assumptions.
Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
Save the inputs that produced an important result so you can reproduce it later.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Match a measured dB headroom to a real resistor pair
Your audio buffer must add 12 dB without clipping the 3.3 V rail. Drop 12 dB into reverse mode, read a voltage gain near 4, and the tool hands you Rf/Rin = 3 for the non-inverting build. Pick Rf = 30k, Rin = 10k, then jump to forward mode to confirm a 0.6 V peak input stays under the rail.
Spot clipping before you breadboard
You set Rf = 47k, Rin = 1k and enter a 0.2 V input. The tool reports an inverting gain of -47 and an ideal output of -9.4 V. On a plus-minus 5 V supply that number screams saturation, so you raise Rin to 10k for a -4.7 gain and a clean -0.94 V before soldering anything.

Common pitfalls

Swapping Rf and Rin. The feedback resistor sits in the numerator, so Rf = 1k, Rin = 10k gives a 0.1 attenuator, not a 10x amp. Check which resistor you typed where before trusting the gain.
Reading the reverse-mode ratio as Rf/Rin for both topologies. For non-inverting, the ratio it returns is Rf/Rin = gain minus 1, so a gain of 5 needs ratio 4, not 5.
Treating the dB figure as a power ratio. The tool uses 20 log10 for voltage gain; if you compare it to a power spec in dB you will be off by a factor of two in the exponent.

Privacy

The gain, the dB conversion, the output voltage and the reverse resistor solve all run as JavaScript inside your browser tab. Resistor values, input voltages and results never reach a server and nothing is logged. Note that the shareable link puts Rf, Rin and your inputs in the URL, so paste the copied text instead of the link when a design is confidential.

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Op-Amp Gain Calculator — Inverting and Non-Inverting

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How Op-Amp Gain Calculator fits into your work

Calculation jobs

Calculation checks

Good next steps

Real-world use cases

Match a measured dB headroom to a real resistor pair

Spot clipping before you breadboard

Common pitfalls

Privacy

FAQ

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