Differential Amplifier Calculator

Work out differential amplifier instantly with clear inputs, formula shown and shareable results.

About Differential Amplifier Calculator

A four-resistor difference amplifier gives Vout = (R2/R1)(V+ - V-) when the ratios match. Resistor mismatch, not the op-amp, usually limits common-mode rejection: with 1% resistors CMRR is capped near 50 dB, which is why matched networks or instrumentation amplifiers are used for small differential signals.

Formula

Difference amplifier

Vout = (R2/R1) x (V+ - V-) when R1/R2 = R3/R4

Worked example

With the default values below, Differential Amplifier Calculator returns Output voltage of 1.00000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Input resistors R1 and R3: 10,000 Ω
Feedback resistors R2 and R4: 100,000 Ω
Non-inverting input: 2.55 V
Inverting input: 2.45 V

Results

Output voltage: 1.00000 V
Differential gain: 10.00 x
Differential input: 100.00 mV
CMRR limit for 1% resistors: 48.79 dB

Step by step

1Values used
2Difference amplifier
3Output voltage= 1.00000 V
4Differential gain= 10.00 x
5Differential input= 100.00 mV
6CMRR limit for 1% resistors= 48.79 dB

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

Frequently Asked Questions

Why is resistor matching so critical?

A ratio mismatch converts common-mode input into output. The achievable CMRR is roughly (1 + gain) divided by four times the fractional tolerance.

When should I use an instrumentation amplifier instead?

Whenever the source impedance is significant or CMRR above about 80 dB is needed — the three-op-amp topology gives high input impedance and trimmed matching.