Op-Amp Resistor Calculator (Inverting / Non-Inverting)

Computes R2, R3, R4 for an inverting or non-inverting amplifier with offset control. Set V2 = 0 if no offset is required. Matches the AllAboutCircuits calculators.

Common: R3 = R1 ,   Vout1 = A·V1 ,   Vout2 = Vout − Vout1

Inverting:

• R2 = −A·R1
• R4 = R3·[((R1+R2)·V2 − Vout2) / (Vout2·R1)]

Non-Inverting:

• R4 = A·R3·(V2 / Vout2)
• R2 = A·(R1+R4)/(R4·R1) − R1

When you need it: Back-solving the feedback pair (Rf/Rg) for a target gain and picking real E-series values that land close to it, for either an inverting or non-inverting stage.

Worked example: Inverting gain −4 needs Rf/Rg = 4: pick Rg = 10 kΩ, Rf = 40.2 kΩ (E96) for −4.02. A non-inverting gain of 4 needs Rf/Rg = 3 → Rf = 30 kΩ, Rg = 10 kΩ.

Tips & gotchas:

• Keep Rg above the source impedance and Rf below ~1 MΩ, or bias current and noise dominate.
• The inverting input is a virtual ground — input impedance equals Rg, unlike the non-inverting case.
• Use 1% (E96) resistors for accurate gain; two 5% parts can stack to several percent of error.
• Add a bias-compensation resistor equal to Rf ∥ Rg at the non-inverting input to cancel bias-current offset.