inverting amplifier calculator - Aaron Graves, PhDude Replica

Inverting Op-Amp Calculator

Input Voltage, V_in (V)

Input Resistor, R_in (Ω)

Feedback Resistor, R_f (Ω)

Positive Output Swing Limit / Rail (V)

Negative Output Swing Limit / Rail (V)

Op-Amp Gain-Bandwidth Product (Hz, optional)

Enter your values and click Calculate.

Assumes an ideal inverting amplifier with virtual ground at the inverting input.

What this inverting amplifier calculator does

This calculator helps you quickly estimate the key behavior of an inverting op-amp circuit. Give it your input voltage and resistor values, and it will compute closed-loop gain, expected output voltage, gain in dB, and current through the input path. If you include output swing limits (rails), it also checks for clipping.

Core formula used

For a classic inverting configuration:

A_v = V_out / V_in = -R_f / R_in

Then the ideal output is:

V_out,ideal = A_v × V_in

The minus sign means the signal is phase-inverted by 180 degrees.

How to use it

Enter your source voltage into V_in.
Set R_in and R_f in ohms.
Enter positive and negative output limits to model saturation behavior.
Add op-amp GBW if you want an approximate closed-loop bandwidth.
Click Calculate.

Example design workflow

Example: target gain of -10

Suppose you want a gain of -10. Pick a convenient input resistor, for example R_in = 10 kΩ. Then set:

R_f = 10 × 10 kΩ = 100 kΩ

If V_in = 0.2 V, ideal output is -2 V. If your amplifier can swing at least ±2 V cleanly, you are not clipping.

Practical engineering notes

1) Keep resistor values in a sensible range

Very low resistors increase loading and power dissipation. Very high resistors increase noise and may worsen offset effects. A common range is roughly 1 kΩ to 100 kΩ depending on application.

2) Bandwidth scales with closed-loop gain

For voltage-feedback op-amps, a quick estimate is: closed-loop bandwidth ≈ GBW / |A_v|. Higher gain means lower bandwidth.

3) Check output swing, not just supply rails

Real devices usually cannot hit the rails exactly unless they are rail-to-rail and lightly loaded. Use realistic swing limits in this calculator for better estimates.

4) Don’t ignore input/output limits

Large input, high gain, or low supply voltage can force clipping. This tool flags clipping so you can adjust resistor ratio or operating range before building.

Quick checklist before prototyping

Gain sign and magnitude are correct for the system.
Output stays inside linear swing limits.
Estimated bandwidth meets your signal requirements.
Resistor values are practical for noise, bias current, and loading.
Power supply and decoupling are appropriate for your op-amp.

Summary

The inverting amplifier is one of the most useful analog building blocks. With just two resistors and an op-amp, you can set accurate gain and get predictable inversion. Use the calculator above to iterate quickly, then validate on the bench with real-device limits in mind.