Op-Amp Voltage Calculator

Compute output voltage, closed-loop gain, and component sensitivity for inverting, non-inverting, and differential op‑amp configurations.

Amplifier Configuration

Local computation only – All calculations run in your browser. No data is transmitted or stored.

Supply rails (saturation check):

V_CC⁺ = V

V_CC^- = V

◯ Op-Amp symbol▭ Resistor▼ Ground➡ Signal flow

Precision Op-Amp Voltage Analysis

The operational amplifier (op-amp) is a fundamental building block of analog electronics. This calculator determines the output voltage (V_out) and closed-loop gain for three essential configurations, assuming ideal op‑amp characteristics: infinite input impedance, zero output impedance, and infinite open-loop gain. The virtual short principle (V₊ = V_-) is applied.

\[ V_{out} = -\frac{R_f}{R_{in}} V_{in} \] | \[ V_{out} = \left(1 + \frac{R_f}{R_g}\right) V_{in} \] | \[ V_{out} = \frac{R_f}{R_1}(V_2 - V_1) \] (matched resistors)

Why Use an Interactive Op-Amp Calculator?

Design Verification: Quickly validate gain and output levels before prototyping.
Educational Clarity: Visualize how resistor ratios affect gain. Perfect for lab preparation and exam revision.
Troubleshooting: Identify saturation issues by comparing calculated output with supply rails (rail‑to‑rail awareness).
Efficiency: Iterate component values instantly without manual formula substitution.

Step-by-Step Derivation & Ideal Assumptions

For an inverting amplifier, the inverting terminal is at virtual ground. Using Kirchhoff’s current law: \( \frac{V_{in} - 0}{R_{in}} = \frac{0 - V_{out}}{R_f} \) → \( V_{out}/V_{in} = -R_f/R_{in} \). The non‑inverting amplifier uses a voltage divider at the inverting node: \( V_- = V_{out} \cdot \frac{R_g}{R_g+R_f} \), and since \( V_+ = V_{in} \), the gain becomes \( 1 + R_f/R_g \). For differential amplifiers, superposition yields the classic difference amplification. Our calculator assumes ideal op‑amp and perfectly matched resistors for differential mode; practical CMRR is discussed in the reference section.

Design Examples & Engineering Cases

Case Study: Sensor Signal Conditioning

A pressure sensor outputs 0–50 mV. To interface with an ADC (0–5V range), an inverting amplifier with gain -100 is needed. Using our calculator: set Rf = 100 kΩ, Rin = 1 kΩ, Vin = 0.05 V → Vout = -5 V. An additional inverting stage corrects polarity. The tool quickly verifies gain accuracy, preventing overdrive. The non‑inverting option avoids phase inversion in DC-coupled systems.

Audio Preamp Design

A non‑inverting amplifier with gain 10 (Rf=9k, Rg=1k) boosts a microphone signal. Using the calculator confirms Vout = 10*Vin, and the high input impedance respects the microphone source. The interactive circuit display helps students understand feedback networks.

Real‑World Component Selection Guide

Resistor values (E96 series): For precision, use 0.1% resistors. Standard 1% E96 values near calculated ratios are acceptable for most applications. Example: desired gain -10 → choose Rf=10kΩ, Rin=1kΩ (both standard).
Op‑amp selection: Low power? Use LM358. Precision DC? Use OP07 (low offset). High speed? Use LM318. Audio grade? Use NE5532. The calculator's ideal model works for all, but real devices have limitations.
Feedback capacitor: For stability, add a small capacitor (5–20 pF) in parallel with Rf to prevent oscillations (dominant pole compensation).

Common Op‑amp Parameters Reference Table

Parameter	LM358 (General purpose)	TL081 (JFET input)	OP07 (Precision)	NE5532 (Audio)
Supply voltage (V)	3–32	7–36	6–36	5–30
Input offset voltage (max)	7 mV	6 mV	0.15 mV	4 mV
Input bias current	45 nA	0.03 nA	1.8 nA	300 nA
Gain-bandwidth product (GBP)	1 MHz	3 MHz	0.6 MHz	10 MHz
Slew rate (V/µs)	0.6	13	0.17	9

Note: The calculator's ideal output assumes the op‑amp's GBP is not limiting the signal frequency. For a closed-loop gain of G and signal frequency f, ensure f < GBP / G to avoid gain roll-off.

Differential Amplifier: CMRR and Resistor Matching

The differential amplifier provides high common-mode rejection only when resistor ratios match precisely: \( \frac{R_f}{R_1} = \frac{R_2}{R_3} \). In practice, use 0.1% matched resistor sets or a single instrumentation amplifier IC. The common‑mode rejection ratio (CMRR) is defined as:

\[ \text{CMRR} = 20 \log_{10}\left( \frac{|A_d|}{|A_{cm}|} \right) \text{ (dB)} \]

With 1% resistors, CMRR typically degrades to ~60 dB, while 0.1% resistors achieve >80 dB. Our calculator assumes ideal matching; for critical applications (e.g., ECG, strain gauges), consider an INA826 or AD8429.

Tool Scope & Limitations

Aspect	Ideal model (this tool)	Real-world limitation
Open-loop gain	Infinite → virtual short exact	Finite A_OL (10⁵–10⁶) causes tiny error
Input impedance	Infinite	BJT inputs: ~1 MΩ; FET: >10¹² Ω; may load high‑impedance sources
Output swing	Any voltage	Rail‑to‑rail types can reach within 50 mV of supply; others lose 1–2 V
Bandwidth	Infinite	Limited by gain‑bandwidth product; use f < GBP/G
Slew rate	Infinite	Limits maximum slope; large signals distort above SR/(2π·V_peak)

Troubleshooting Common Discrepancies

Measured Vout lower than calculated: Check if output is saturated (see saturation warning). Reduce gain or increase supply voltage.
Unexpected DC offset: Op‑amp input offset voltage and bias currents create error; use precision op‑amp or add offset nulling.
Oscillations / noise: Add a small capacitor (100 pF) across Rf. Ensure proper decoupling (0.1 µF + 10 µF near supply pins).
Differential output not matching V2-V1: Resistor mismatch (use matched pairs) or common‑mode voltage exceeds input range.
Gain changes with frequency: The op‑amp’s gain‑bandwidth product limits high‑frequency gain; simulate with real op‑amp model.

Gain & Output Reference Table

Configuration	Gain Equation	Example Values	Output (Vin=0.2V)
Inverting	-Rf/Rin	Rf=10k, Rin=1k → Gain -10	-2.00 V
Non‑Inverting	1+Rf/Rg	Rf=9k, Rg=1k → Gain 10	2.00 V
Differential	Rf/R1 (V2-V1)	Rf=10k, R1=1k, V2=0.5V, V1=0.2V → Gain 10	3.00 V

Rooted in Analog Excellence – This tool follows fundamental principles from "Art of Electronics" (Horowitz & Hill) and industry standards (Texas Instruments Op Amp Applications Handbook). The implementation uses symbolic algebra and verified against SPICE simulations. last updated May 2026.

Frequently Asked Questions

In an inverting amplifier with negative feedback, the non-inverting input is grounded, forcing the inverting input to nearly 0V due to high open-loop gain. This virtual ground simplifies current analysis.

This version focuses on single/differential inputs. For summing amplifiers, Vout = -Rf*(V1/R1 + V2/R2 + ...). Extending the inverting configuration handles multiple inputs.

The ideal op-amp would produce that voltage, but real devices saturate near the supply rails. Always check your Vout against the op‑amp’s output swing specifications.

Assuming perfectly matched resistors (R1=R3, Rf=R2) and ideal op‑amp, Vout = (Rf/R1)*(V2-V1). Real-world CMRR depends on matching; use 0.1% resistors for high precision.

References: TI "Op Amps for Everyone"; Analog Devices MT-033 Tutorial; Electronics Tutorials.