Op Amp Gain Calculator - Inverting & Non-Inverting Gain

An op amp gain calculator is a quick way to find the closed-loop voltage gain of an operational amplifier circuit from the two resistors that set the feedback network, and it tells you whether the output is in phase with the input or flipped 180 degrees.

• • Design an audio pre-amplifier: Pick Rin and Rf so a microphone or line-level signal lands at the ADC input range without clipping.
• • Build a summing or difference amplifier: Set the feedback and input resistors so the per-channel gain matches what your signal chain expects.
• • Verify a non-inverting buffer: Check that a unity-gain follower delivers a gain of 1 with 0° phase before a high-impedance sensor.
• • Translate gain into decibels for an RF chain: Convert the voltage gain magnitude into dB so a stage matches the budget of an antenna or mixer datasheet.

Operational amplifiers are the workhorses of analog signal conditioning, and almost every circuit starts with the two resistor values that set the closed-loop gain. The same math covers a TL072 audio pre-amp, an LM358 sensor front end, and a precision OPA227 instrumentation channel.

The calculator also prevents the most common sign mistake: inverting and non-inverting configurations share the same gain magnitude when the resistor ratio matches, but the polarity is opposite, which decides whether the next stage sees a positive or negative version of your signal.

When you only need to step a supply voltage down, the voltage divider calculator gives the unloaded Vout from two resistors using the same ratio math that op-amps rely on for feedback.

The calculator evaluates two textbook gain equations, one for the inverting configuration and one for the non-inverting configuration, and reports the magnitude in linear units and decibels alongside the output phase.

• R_in (or R1): Resistor between the input source and the op-amp inverting terminal. It sets the input impedance and is the gain-ratio denominator.
• R_f (or R2): Feedback resistor between the op-amp output and the inverting input. The R_f / R_in ratio sets the gain magnitude.
• Configuration: Whether the input goes to the inverting terminal (inverting, gain negative) or the non-inverting terminal (non-inverting, gain positive).

Both equations assume the op-amp's open-loop gain is large enough that any difference between the two inputs is amplified until it is essentially zero. With negative feedback through R_f, the inverting input tracks the non-inverting input, and the algebra collapses to a simple resistor ratio.

Once the linear gain is known, the calculator takes its absolute value and applies the 20 log10 voltage rule to express the result in decibels. The sign is dropped because dB describes magnitude only, and the phase column carries polarity separately.

According to Wikipedia (Operational amplifier), the voltage gain of an inverting op-amp is A_v = -R_f / R_in and the gain of a non-inverting op-amp is A_v = 1 + R_2 / R_1, with the negative sign indicating the 180° phase inversion.

Pick Rin and Rf with standard E12 or E24 values and check the actual load behavior with the electrical resistance calculator before you place the parts on a breadboard.

Four ideas show up in every op-amp gain discussion; understand these once and the rest of the page reads itself.

These four ideas are enough to read any op-amp datasheet, because input offset voltage, gain-bandwidth product, and slew rate all describe how the closed-loop gain behaves at the edges of real device performance.

According to Wikipedia (Negative-feedback amplifier), applying negative feedback trades open-loop gain for predictable closed-loop gain, wider bandwidth, and lower distortion.

If your gain figure needs to land on a 50 Ω or 75 Ω RF load in dBm instead of dB, the dBm to watts calculator applies the same 20 log10 voltage rule to translate the gain into a power level.

Five quick steps take you from a resistor pair to a complete gain, magnitude, decibel, and phase result.

1. 1 Pick the op-amp configuration: Select Inverting if the signal goes through Rin into the inverting terminal, or Non-Inverting if it goes into the non-inverting terminal.
2. 2 Enter the input resistance: Type Rin (inverting) or R1 (non-inverting) in ohms. The 1 kΩ default is a sensible starting point for low-impedance audio and sensor signals.
3. 3 Enter the feedback resistance: Type Rf (inverting) or R2 (non-inverting) in ohms. Set Rf to 0 Ω for a unity-gain non-inverting buffer.
4. 4 Read the linear gain and magnitude: Voltage Gain shows the signed result (negative for inverting, positive for non-inverting); Gain Magnitude strips the sign for comparison with datasheet numbers.
5. 5 Check the decibel and phase values: Use Gain in Decibels for RF budgets. Confirm the phase is 180° for inverting or 0° for non-inverting before connecting downstream stages.

A microphone pre-amp uses an inverting op-amp with Rin = 2.2 kΩ and Rf = 47 kΩ. The calculator returns about -21.4× gain, 21.4× magnitude, 26.6 dB, and 180° phase, which fits a dynamic microphone running into a line-level ADC input.

For an audio load, the rms-to-watts calculator turns the post-amp RMS voltage into continuous watts so you can match amplifier headroom to the speaker rating.

Six practical benefits explain why this calculator saves time compared with working the formulas by hand or relying on a SPICE simulator.

• • Cuts resistor-pair mistakes: Pairs the two gain formulas on one screen so you cannot accidentally swap them.
• • Returns all four useful outputs at once: Shows signed gain, magnitude, decibels, and phase together so you can paste any into a design log.
• • Works with any resistor pair: Accepts Rin and Rf from 1 Ω up to 10 MΩ, so it covers audio, instrumentation, and RF front ends without preset menus.
• • Highlights polarity risk: Forces you to read the phase column, the most common source of polarity bugs in mixed-signal designs.
• • Supports back-of-envelope RF budgets: Converts linear gain into decibels using the same 20 log10 rule RF engineers use, so the result drops into a link budget or noise figure calculation unchanged.
• • Reinforces the dB rule: Shows the 20 log10 conversion for every result, which trains the right habit for the rest of an analog or RF design career.

For matched-impedance lines, the RF unit converter applies the same 20 log10 voltage rule to convert the post-amp voltage into dBm at the load so the link budget stays consistent end to end.

Five factors decide whether the calculator's result matches the gain you measure on the bench, and two limitations tell you when to reach for a more detailed analysis.

• • The closed-loop formulas assume an ideal op-amp with infinite open-loop gain and zero output impedance, so the calculator does not model finite GBW, slew rate, or output stage limits. Use SPICE for those effects.
• • The decibel output uses the 20 log10 voltage rule, which assumes a high-impedance sensor or ADC input. For matched-impedance RF stages, convert to dBm with the appropriate reference impedance.

According to All About Circuits (Introduction to the Decibel), op-amp gain in decibels equals 20 log10 of the magnitude because voltage is a field quantity and uses the 20 multiplier rather than 10.

To convert that dB figure back into a linear ratio or add two gain stages in dB, the decibel calculator applies the same 20 log10 voltage rule with dB-addition math.