Op-Amp Gain Calculator

The operational amplifier was born in analog computing at Bell Labs in the 1940s. Loebe Julie, George Philbrick, and the MIT Rad Lab team built the first vacuum-tube op-amps to perform mathematical "operations" — addition, subtraction, integration, differentiation — for fire-control computers and later general analog computation. The name "operational amplifier" stuck because those computers solved differential equations by cascading op-amp integrators with adjustable gains.

The first monolithic (single-chip) op-amp — Bob Widlar\'s µA702 at Fairchild in 1964 — changed the game. His follow-up, the µA741 (1968), became the most produced analog IC in history: a two-input, single-output amplifier with near-ideal characteristics (high gain, high input impedance, low output impedance) for a few cents per unit. The inverting and non-inverting feedback topologies this calculator models were described by Harry Black (feedback inventor, 1927) and popularized in George Philbrick\'s 1953 Philbrick Applications Manual — the first engineering text to treat the op-amp as a reusable building block.

Modern op-amps have specialized descendants: chopper-stabilized for precision (nanovolt Vos), JFET-input for very low bias current, rail-to-rail for single-supply operation, high-speed for video and RF. But the gain equations A = 1 + Rf/Rin (non-inverting) and A = −Rf/Rin (inverting) are unchanged since Philbrick\'s manual — they follow directly from assuming infinite open-loop gain and zero input current, and they work on every op-amp you\'ll ever use.

Pick inverting or non-inverting topology, enter R_in and R_f with engineering suffixes, and optionally a V_in. The tool returns voltage gain (both V/V and dB), output voltage, and a circuit-diagram visualization of the chosen topology.

Keep resistor values in the 1 kΩ–100 kΩ range as a rule of thumb — too low loads the op-amp\'s output stage, too high introduces noise and bias-current errors. For gain > 100 at signal frequencies above audio, check the op-amp\'s gain-bandwidth product: 1 MHz GBW at A = 100 gives only 10 kHz of usable bandwidth. Everything runs client-side; no values leave your browser.