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Inverting Op-Amp Resistor Calculator

R2 = |G|·R1 and R3 = R1. G = −10 with R1 = 10 kΩ gives 100 kΩ.

By Jasper · Updated

Calculator

PASS100 kΩR3 10 kΩ

R2 = |G| · R1 and R3 = R1 (bias-current compensation). G must be negative — use the op-amp gain calculator for G ≥ 0. Optional V2 and Vout2 solve level-shift R4.

R2
100 kΩ
R3
10 kΩ
Nearest E24
100 kΩ
Nearest E96
100 kΩ
  • Pass Feedback R2: R2 = |G| · R1 = 100000 Ω
  • Pass Bias R3: R3 = R1 = 10000.0 Ω (bias-current compensation)

Formula

Feedback

R2=|G|R1 R2 = |G| · R1

Bias compensation

R3=R1 R3 = R1 (bias-current compensation)

Level-shift R4

R4=R3(R1+R2)V2-Vout2Vout2R1 R4 level-shift (utmel algebra)

Variables

Symbol Meaning Unit Typical range Precision Default
G Target gain — ≤ 0 G must be < 0 4 sig -10
R1 Input resistor Ω ≥ 0 mΩ 4 sig 10 kΩ
Vin Vin (optional) V — 4 sig 0.1 V
V2 Bias V2 (optional) V — 4 sig
Vout2 Shifted Vout2 (optional) V — 4 sig
R2 Feedback Ω — 4 sig —
R3 Bias compensation Ω — 4 sig —
R2E24 Nearest E24 Ω — 4 sig —
R2E96 Nearest E96 Ω — 4 sig —
GE24 Gain with E24 — — 4 sig —
GE96 Gain with E96 — — 4 sig —
Vout Vout = G·Vin V — 4 sig —
R4 Level-shift Ω — 4 sig —
ok R4 realizable — — 1 sig —

Worked example

G = −10, R1 = 10 kΩ

Input Value
G · Target gain -10
R1 · Input resistor 10 kΩ
Vin · Vin (optional) 0.1 V
Output Value
R2 · Feedback 100 kΩ
R3 · Bias compensation 10 kΩ
R2E24 · Nearest E24 100 kΩ
R2E96 · Nearest E96 100 kΩ
Vout · Vout = G·Vin -1 V

G = −4.7, R1 = 1 kΩ (exact E24)

Input Value
G · Target gain -4.7
R1 · Input resistor 1 kΩ
Output Value
R2 · Feedback 4.7 kΩ
R2E24 · Nearest E24 4.7 kΩ

How it works

Pick R1 first (noise vs input current), then R2 falls out of the gain. R3 equals R1 so the two inputs see the same DC resistance. Optional V2/Vout2 solve a single level-shift resistor; if that resistor comes out negative, the bias is not possible with this topology.

Pitfalls

  • Entering a positive G. This topology inverts; use the op-amp gain page for G ≥ 0.
  • Forcing a level shift that needs R4 ≤ 0 — that bias is not realizable with this network.
  • Snapping R2 to E24 and forgetting the gain moves.

FAQ

What resistors give G = −10 with R1 = 10 kΩ?

R2 = 100 kΩ and R3 = 10 kΩ.

Why must G be negative?

An inverting stage has G = −R2/R1. Non-inverting designs belong on the op-amp gain page.

What does R3 do?

It matches the DC resistance seen by the +input to R1, cancelling bias-current offset.

When is R4 not realizable?

When the algebra returns R4 ≤ 0 for the requested V2 and Vout2.

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