Productive ToolboxOp-Amp Calculator
Calculate gain and output voltage for operational amplifier circuits including inverting, non-inverting, voltage follower, and summing amplifier configurations.
Op-Amp Calculator
Calculate gain and output voltage for operational amplifier circuits. Supports inverting, non-inverting, voltage follower, and summing amplifier configurations.
Actions
Circuit Configuration
Input Parameters
Common Examples
What Is an Op-Amp Calculator?
An op-amp calculator is a free electronics tool that finds the voltage gain and output voltage of an operational amplifier circuit from its resistor values and input voltage. It covers the four configurations that form the foundation of analog design — inverting amplifier, non-inverting amplifier, voltage follower, and summing amplifier — and answers the question every analog designer starts with: what output voltage will this resistor network and input signal produce?
Op-amp gain formulas look deceptively simple, but small mistakes are common: forgetting the sign flip on an inverting stage, assuming non-inverting gain can attenuate when it can only amplify, or mixing up resistor units between kΩ and Ω. This calculator applies the correct ideal op-amp formula for whichever configuration you're working with and shows every step of the math.
This operational amplifier calculator is built for electronics students learning op-amp theory, circuit designers prototyping analog front-ends, audio engineers building mixer and buffer stages, and hobbyists checking a breadboard build against the expected output. It supports all four circuit types, includes built-in presets for each, saves your last 10 calculations, and runs entirely in your browser — free, with no signup required.
How Op-Amp Gain Calculation Works
Core Formulas by Configuration
Inverting: Gain = −(R2 ÷ R1) · Vout = Gain × Vin
Non-Inverting: Gain = 1 + (R2 ÷ R1) · Vout = Gain × Vin
Voltage Follower: Gain = 1 · Vout = Vin
Summing: Vout = −Rf × (V1÷R1 + V2÷R2 + V3÷R3)
- Virtual ground: negative feedback forces the inverting input to sit at the same voltage as the non-inverting input — the assumption every one of these formulas relies on
- Sign convention: inverting and summing configurations always flip the output's polarity; non-inverting and voltage follower configurations preserve it
- Gain floor: non-inverting gain can never fall below 1 since the formula is always 1 plus a positive ratio; inverting gain has no such floor and can attenuate as well as amplify
- Resistor units: each resistor can be entered independently in Ω, kΩ, or MΩ — the calculator normalizes everything to ohms before computing
- Ideal assumptions: all formulas assume an ideal op-amp with infinite open-loop gain and infinite input impedance — real output is still limited by the supply rails
How to Use the Op-Amp Calculator
Step-by-Step Guide
- 1Select an op-amp configuration: Choose inverting, non-inverting, voltage follower, or summing amplifier from the mode selector. The input fields update automatically to match what that configuration needs.
- 2Enter your resistor values: Input R1 and R2 for inverting or non-inverting mode, or Rf plus one to three input resistors for the summing amplifier. Choose Ω, kΩ, or MΩ independently for each resistor.
- 3Enter the input voltage: Type Vin for inverting, non-inverting, or voltage follower mode, or up to three input voltages (Vin1, Vin2, Vin3) for the summing amplifier.
- 4Try a built-in preset: Load a preset such as Gain of -10, Gain of 11, or 3-Input Mixer to see realistic resistor values before entering your own design.
- 5Read the gain and output voltage: The calculator instantly returns the voltage gain and Vout, along with a full step-by-step breakdown showing exactly how each formula was applied.
- 6Export or save your calculation: Copy the result to your clipboard or export a text report. The last 10 calculations are saved automatically for comparing different configurations.
What This Tool Provides
- ✓Real-time gain and Vout calculation as you type
- ✓4 configurations: inverting, non-inverting, follower, summing
- ✓Independent Ω / kΩ / MΩ units per resistor
- ✓Up to 3 weighted inputs for summing amplifiers
- ✓Full step-by-step formula breakdown
- ✓Built-in presets for every configuration
- ✓Calculation history (last 10 entries saved)
- ✓Export results as a text report
- ✓Copy result to clipboard
- ✓100% browser-based — no data sent to a server
Real-World Use Cases
Audio Phase-Inverting Stage
An audio engineer needs to invert a 1V line-level signal by 10× for a mixing console's phase-flip channel. Using Inverting mode with R1 = 1 kΩ, R2 = 10 kΩ, Vin = 1V, the calculator returns Gain = −10 and Vout = −10V — confirming the correct polarity flip and magnitude.
Weak Sensor Signal Amplification
A circuit designer needs to boost a 100 mV sensor output to a usable ADC input range. Using Non-Inverting mode with R1 = 1 kΩ, R2 = 100 kΩ, Vin = 0.1V, the calculator returns Gain = 101 and Vout = 10.1V — well within a typical 0–12V ADC input range.
High-Impedance Sensor Buffer
A hobbyist is buffering a high-impedance photodiode output before feeding it into a low-impedance ADC input. Using Voltage Follower mode with Vin = 3.3V, the calculator confirms Gain = 1 and Vout = 3.3V — the signal passes through unchanged while gaining drive strength.
2-Channel Audio Mixer
An audio hobbyist is combining two 1V line-level channels into a single mix bus. Using Summing mode with Vin1 = 1V, Vin2 = 1V, Rf = 10 kΩ, Ri1 = 10 kΩ, Ri2 = 10 kΩ, the calculator returns Vout = −2V — the two signals summed and inverted equally.
Weighted Summing DAC Stage
An electronics student is building a simple 2-bit weighted summer where the second channel should contribute twice the weight of the first. Using Summing mode with Vin1 = 1V, Vin2 = 1V, Rf = 10 kΩ, Ri1 = 10 kΩ, Ri2 = 5 kΩ, the calculator returns Vout = −3V — channel 1 contributes −1V and channel 2 contributes −2V to the total.
Unity-Gain Signal Inverter
An engineer needs to flip the polarity of a 5V control signal without changing its magnitude, for a downstream circuit expecting a negative reference. Using Inverting mode with R1 = 10 kΩ, R2 = 10 kΩ, Vin = 5V, the calculator returns Gain = −1 and Vout = −5V — an exact sign flip with no attenuation or amplification.
Tips & Common Mistakes
Pro Tips
- 💡Remember non-inverting gain is always ≥ 1 since the formula is 1 + (R2/R1) — you can never attenuate a signal in this configuration. If you need gain below 1, switch to an inverting amplifier with R2 smaller than R1, or use a passive voltage divider instead.
- 💡In the inverting configuration, R1 also sets the input impedance seen by the source (Zin ≈ R1). Choose R1 large enough not to load down a high-impedance source, but not so large that the op-amp's input bias current introduces a meaningful offset error.
- 💡Use a voltage follower whenever you need to isolate a high-impedance source — like a sensor, photodiode, or piezo element — from a low-impedance load, without adding gain or inverting the signal.
- 💡In a summing amplifier, each input's weight is set purely by its own resistor ratio (Rf/Rn), completely independent of the other inputs. This lets you mix multiple signals with different gains simultaneously without them interacting with each other.
- 💡Check your computed Vout against your real supply rails before building the circuit. An ideal formula will happily return 15V from a design running on ±12V rails — the real op-amp will simply clip a couple volts below the rail instead of reaching that value.
- 💡Prefer standard resistor values — 1k, 2.2k, 4.7k, 10k, 100k — over solving for an exact non-standard ratio. Since gain depends only on the ratio between resistors, scaling both up or down by the same factor gives the same gain with easier-to-source parts.
Common Mistakes to Avoid
- ✕Don't forget the sign on an inverting amplifier. A 'gain of 10' inverting stage produces an output 10× larger in magnitude but flipped in polarity — treating it as a same-sign gain like a non-inverting stage is one of the most common beginner mistakes.
- ✕Don't assume R1 and R2 share the same unit. This calculator lets you set Ω, kΩ, or MΩ independently per resistor — entering '100' meaning 100 kΩ into a field set to Ω throws the computed gain off by a factor of 1,000.
- ✕Don't leave a summing amplifier's unused input resistor at zero instead of leaving that channel unfilled — a resistor value of zero causes a divide-by-zero in the Vn/Rn term, not a channel that simply contributes nothing.
- ✕Don't expect a voltage follower to provide any amplification. It exists purely to buffer and isolate — if your design needs gain, use a non-inverting configuration with an appropriate R1/R2 ratio instead.
- ✕Don't treat the ideal-op-amp formulas as the final word for precision designs. Real op-amps have finite open-loop gain, input offset voltage, and bias current — for high-precision or low-gain designs, cross-check your resistor choices against the actual op-amp's datasheet specs.
Op-Amp Configuration Comparison
| Configuration | Gain Formula | Inverts Signal? | Input Impedance | Typical Use |
|---|---|---|---|---|
| Inverting | −(R2 ÷ R1) | Yes | ≈ R1 | Signal inversion, attenuation, mixing |
| Non-Inverting | 1 + (R2 ÷ R1) | No | Very high | Sensor & instrumentation preamps |
| Voltage Follower | 1 | No | Very high | Buffering, impedance isolation |
| Summing | −Rf ÷ Rn per input | Yes | ≈ Rn per input | Audio mixers, weighted DACs |
* All formulas assume an ideal op-amp with infinite open-loop gain and infinite input impedance. Real output voltage is limited by the actual supply rails.
Frequently Asked Questions
What is an op-amp calculator?
An op-amp calculator finds the voltage gain and output voltage of an operational amplifier circuit from its resistor values and input voltage. It covers four standard configurations — inverting amplifier, non-inverting amplifier, voltage follower, and summing amplifier — the building blocks nearly every analog circuit is made from.
How is gain calculated for an inverting amplifier?
The inverting amplifier's gain is Gain = −(R2 ÷ R1), where R2 is the feedback resistor and R1 is the input resistor. The negative sign means the output is inverted — 180° out of phase with the input. Output voltage is then Vout = Gain × Vin, so a gain of −10 with a 1V input produces a −10V output.
How is gain calculated for a non-inverting amplifier?
The non-inverting amplifier's gain is Gain = 1 + (R2 ÷ R1), where R2 is the feedback resistor to the output and R1 connects the inverting input to ground. Because the formula always adds 1, non-inverting gain can never drop below 1 — it can only amplify, never attenuate, and the output stays in phase with the input.
What is a voltage follower and when do I use one?
A voltage follower, also called a unity gain buffer, has Vout = Vin with a gain of exactly 1. It provides very high input impedance and very low output impedance without adding any amplification, which makes it the standard way to isolate a high-impedance source — like a sensor or photodiode — from a low-impedance load without loading it down.
How does a summing amplifier combine multiple inputs?
A summing amplifier computes Vout = −Rf × (V1/R1 + V2/R2 + V3/R3 + ...), where each input has its own resistor. Each channel's contribution to the output is scaled independently by the ratio Rf/Rn, so you can mix several signals together with different weights simultaneously, and the result is inverted just like a single-input inverting amplifier.
Why is the inverting amplifier's output voltage negative for a positive input?
The inverting configuration feeds the input signal through R1 into the op-amp's inverting terminal, and negative feedback through R2 forces that terminal to a virtual ground. This topology inherently flips the signal's polarity — a positive input produces a negative output and vice versa — which is why the gain formula always carries a minus sign.
What is the difference between inverting and non-inverting amplifier input impedance?
The inverting amplifier's input impedance is approximately equal to R1, because the source drives current through R1 into the virtual ground node. The non-inverting amplifier's input impedance is extremely high — essentially the op-amp's own input impedance — because the signal connects directly to the non-inverting terminal, which draws negligible current.
Can non-inverting gain ever be less than 1?
No. Because the formula is Gain = 1 + (R2 ÷ R1), the smallest possible non-inverting gain is 1, which occurs only when R2 = 0 (making it a voltage follower). If you need a gain below 1 — attenuation — use an inverting amplifier with R2 smaller than R1, or a passive voltage divider instead.
What happens if I request a gain the real op-amp can't reach?
This calculator uses ideal op-amp formulas, which assume infinite open-loop gain and unlimited output swing. A real op-amp's output voltage is limited by its supply rails — typically 1 to 2V below each rail — so if the calculated Vout exceeds what your actual supply voltage allows, the real circuit will clip well before reaching that theoretical value.
Is my data private when using this calculator?
Yes. All calculations run entirely in your browser using JavaScript. Your resistor values, input voltages, and any saved calculation history are never transmitted to any server, stored in any database, or accessible to anyone other than you.
Who Uses This Op-Amp Calculator?
Electronics Students
Work through inverting, non-inverting, and summing amplifier problems from coursework, checking hand-solved gain and Vout values before an exam or lab report.
Circuit Designers
Prototype analog front-end stages and verify resistor ratios produce the target gain before committing values to a schematic or PCB layout.
Audio Engineers
Design mixer summing stages, buffer stages, and phase-inverting circuits, calculating exact resistor ratios needed for a target mix level.
Electronics Hobbyists
Check a breadboard op-amp build against the expected output voltage, using presets to confirm the calculator matches known reference designs first.
Maker & Robotics Hobbyists
Buffer sensor signals with a voltage follower or amplify weak analog readings with a non-inverting stage before feeding a microcontroller's ADC.
Electrical Engineers
Cross-check hand calculations or SPICE simulation results for op-amp stages during design review, catching sign or resistor-unit errors quickly.