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Non-Inverting Amplifier Gain Calculator

Enter the feedback and ground resistors to find the non-inverting amplifier gain.

How it is calculated

For an ideal op-amp in the non-inverting configuration the gain depends only on the two resistors: Av = 1 + Rf ÷ Rg, where Rf is the feedback resistor (output to inverting input) and Rg the resistor from the inverting input to ground, both in ohms. The decibel value is dB = 20 × log10(Av). If you enter an input voltage in volts the tool also gives Vout = Av × Vin. Only the ratio matters, so kΩ work as well as Ω if both use the same unit. Rg must be above zero and Rf cannot be negative; otherwise there is no result. Rf = 0 gives a gain of exactly 1 (a voltage follower). The tool assumes an ideal op-amp: it ignores supply limits, bandwidth, input offset and loading, so the real output cannot exceed what the supply rails allow.

Worked example

Take Rf = 47 kΩ, Rg = 10 kΩ and an input of 0.2 V. Gain = 1 + 47,000 ÷ 10,000 = 1 + 4.7 = 5.700 V/V. In decibels: 20 × log10(5.7) = 20 × 0.7559 = 15.12 dB. Output = 5.7 × 0.2 = 1.140 V. A 0.2 V sensor signal is therefore raised to 1.14 V, which a typical single-supply op-amp can deliver.

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Common mistakes

  • Using Rf ÷ Rg alone as the gain, which is the inverting amplifier formula. The non-inverting circuit adds 1, so equal resistors give a gain of 2, not 1.
  • Swapping Rf and Rg. With Rf = 10 kΩ and Rg = 47 kΩ the gain is only 1.213, not 5.7. Rf is the resistor between output and inverting input.
  • Mixing units, such as Rf in kΩ and Rg in Ω. Both must be in the same unit, otherwise the ratio, and so the gain, is wrong by a factor of 1000.
  • Trusting the output voltage beyond the supply. An input of 3 V with this gain shows 17.1 V, but a circuit on a 5 V or 12 V supply clips well before that.
  • Expecting gain below 1. This circuit cannot attenuate: even with Rf = 0 the gain is 1.000, and a negative Rf gives no result, because a resistor cannot have a negative value.

About this calculator

A non-inverting op-amp circuit feeds the input directly into the amplifier's positive terminal, with a feedback resistor Rf and a ground resistor Rg forming a voltage divider around the negative terminal. Because the op-amp forces its two inputs to the same voltage, the closed-loop voltage gain works out to Av = 1 + Rf/Rg — always greater than or equal to 1, unlike an inverting configuration. In decibels that same gain is expressed as dB = 20·log₁₀(Av).

This calculator takes the feedback and ground resistor values (and optionally an input voltage) and returns the gain, its decibel value, and the resulting output voltage. Electronics engineers and hobbyists use it when designing preamplifiers, sensor signal-conditioning stages, and instrumentation amplifiers where high input impedance and a non-inverted output are required, picking Rf and Rg to hit a target gain before ever touching a breadboard.

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Comments (1)

  • Editorial team

    The gain here comes from the resistors alone, and a real op-amp adds a limit this tool does not model: for a typical voltage-feedback part the usable bandwidth is roughly its gain-bandwidth product divided by the closed-loop gain. With a 1 MHz part and a gain of 11, expect about 90 kHz. Standard resistor values also shift the gain, since 9.1 kΩ over 1 kΩ gives 10.1, not 10. What signal frequency are you amplifying?

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