Op-Amp Gain Calculator

An op-amp gain calculator that handles all five standard configurations — non-inverting, inverting, voltage follower, difference amplifier, and transimpedance — and goes beyond simple V/V gain to give you a complete bandwidth budget. Enter resistor values with SI prefixes (10k, 100k, 4.7M), read off gain in V/V and dB, then expand the bandwidth panel to add your op-amp’s GBW product and slew rate for an accurate picture of your signal chain’s frequency limits.

How it works

An operational amplifier is a high-gain differential voltage amplifier. With a few external resistors the gain is set precisely by the feedback network, making it the most versatile analogue building block in electronics.

Non-inverting configuration

The input is applied to the non-inverting (+) pin. Resistor Rg connects the inverting (−) pin to ground, and Rf connects the output back to the inverting pin:

Av = 1 + Rf / Rg

The gain is always ≥ 1, the output is in phase with the input, and the input impedance is very high (limited only by the op-amp’s differential input bias current, typically tens of megohms for a JFET-input part such as the TL072).

Inverting configuration

The input is applied through Rg to the inverting (−) pin while Rf provides feedback:

Av = −Rf / Rg

The magnitude of gain can be any positive value, but the output is 180° out of phase. Input impedance equals Rg, so this matters when driving the stage from a source with significant output resistance. Setting Rf = Rg gives unity gain with inversion — a handy sign inverter.

Voltage follower

When output is connected directly to the inverting input (Rf = 0, Rg → ∞) the gain is exactly 1 V/V (0 dB). No calculation is needed, but the high input impedance and low output impedance make it an ideal buffer between stages without signal attenuation.

Difference amplifier

With four matched resistors — R1 = R3 = Rg and R2 = R4 = Rf — the circuit subtracts one voltage from another:

Vout = (Rf / Rg) × (V+ − V−)

CMRR (common-mode rejection ratio) depends critically on resistor matching; a 1% mismatch can reduce CMRR to around 40 dB. For precision differential measurements, use 0.1% resistors or an integrated instrumentation amplifier (INA).

Transimpedance (current-to-voltage) amplifier

A photodiode or other current source drives the inverting input directly, with Rf providing feedback. The inverting input sits at virtual ground:

Vout = −Iin × Rf (transimpedance = −Rf, in Ω or V/A)

Common choices: 1 MΩ for low-light photodiode receivers, 1 kΩ–10 kΩ for high-speed applications where capacitance at the input node would otherwise limit bandwidth.

Bandwidth

Two separate mechanisms limit the usable frequency range:

GBW product: Every unity-gain-stable op-amp has a constant gain–bandwidth product. At closed-loop gain |Av|:

f−3dB = GBW / |Av|

A 1 MHz GBW op-amp (e.g. LM741) set to ×10 has only 100 kHz bandwidth. A 10 MHz part (e.g. TL072) at ×10 gives 1 MHz. For audio or signal-chain work, budget for at least 5× headroom (bandwidth ≫ highest signal frequency).

Slew-rate limit: For large-amplitude signals, the output voltage can only change at a rate of SR V/µs. The slew-rate limited full-power bandwidth is:

f_max = SR / (2π × Vpeak)

The calculator takes the minimum of the two limits as the effective bandwidth — the constraint that will bite first in practice.

Worked example

Non-inverting audio pre-amp with gain of 11×:

• Set Rf = 100 kΩ, Rg = 10 kΩ
• Av = 1 + 100k/10k = 11 V/V = 20.83 dB
• Op-amp: NE5532 (GBW ≈ 10 MHz, SR ≈ 9 V/µs)
• GBW-limited bandwidth: 10 MHz / 11 = 909 kHz ✓ (well above 20 kHz audio)
• SR-limited BW at Vpeak = 10 V: 9×10⁶ / (2π × 10) ≈ 143 kHz ← actual limit
• To push SR-limit above 100 kHz at 10 V, choose an op-amp with SR > 6.3 V/µs

Every calculation runs entirely in your browser — nothing is ever uploaded or stored.