Non-Inverting Op-Amp Resistor Calculator: enter your target gain, input signal, and supply rails to solve exact R1, R2, and offset resistor values, then check output clipping risk.
Why Gain Depends on R2 Divided by R1, Not R2 Alone
A non-inverting amplifier takes an input signal into the op-amp’s positive input and sets the output gain with two resistors forming a voltage divider from the output back to the negative input. This is Ohm’s law applied to a feedback loop, not a code or standard — R1 runs from the negative input down to ground, R2 runs from the negative input to the output, and their ratio fixes how hard the amplifier pushes the output to keep both inputs at the same voltage.
The base relationship is:
$$Gain = 1 + \frac{R_2}{R_1}$$
Rearranged for the resistor you’re usually solving for:
$$R_2 = R_1 \times (Gain – 1)$$
$R_1$ is the resistor from the inverting input to ground, chosen first since everything else scales from it. $R_2$ is the feedback resistor. $Gain$ is the ratio between output voltage and input signal voltage that you want. This part of the calculation is the whole story when your input signal, scaled by your target gain, already lands on the output voltage you want.
Solving R2 for a 6V Output From a 1V Signal With a 5V Offset
Say your input signal V1 sits at 1V, you want an overall gain of 2 V/V, and you’ve fixed R1 at 10 kΩ. Straight gain alone gets you to 2V — but your target output is 6V. That 4V gap is where a second reference voltage, V2, comes in. Feed it 5V and the calculator works out how much of that 5V needs to reach the output to close the gap.
The required contribution from V2 is $(6 – 2 \times 1) / 5 = 0.8$ V/V. Because that number is positive, the offset gets summed in at the non-inverting side rather than the inverting side, and the feedback resistor absorbs both the signal gain and the offset gain at once:
$$R_2 = R_1 \times (Gain + A_{V2} – 1) = 10 \times (2 + 0.8 – 1) = 18.00\text{ k}\Omega$$
That 18 kΩ is the headline number. The rest of the circuit — the two resistors that actually blend V1 and V2 onto the non-inverting input before that gain is applied — comes out of the same math:
| Resistor | Bias-balanced value | Simplified value |
|---|---|---|
| R2 (feedback) | 18.00 kΩ | 18.00 kΩ |
| R3 (from V1) | 9.00 kΩ | 10.00 kΩ |
| R4 (from V2) | 22.50 kΩ | 25.00 kΩ |
The bias-balanced pair is sized so R3 and R4 in parallel equal 6.43 kΩ — the same resistance the feedback network (R1 parallel with R2) presents at the inverting input. Matching those two values means both op-amp inputs see roughly the same source resistance, which cancels out most of the output error caused by input bias current. The simplified pair skips that matching and just sets R3 equal to R1, which is easier to build but leaves a small bias-current-driven offset uncorrected.
The closed-loop gain from V1 alone, once R2 is set this way, works out to 2.80 V/V rather than the 2 V/V you asked for — the extra 0.8 comes from the offset term sharing the same feedback path. The feedback fraction, R1 divided by R1 plus R2, comes out to 35.71%, which is the number that governs how much of your op-amp’s open-loop gain and bandwidth this configuration actually uses.
Why Vout Must Stay Inside the Supply Rails
With ±15V supplies and a 6V target output, there’s 9.00V of headroom to the positive rail and 21.00V of headroom to the negative rail. Neither of those can go to zero or below without the amplifier clipping. This isn’t a soft guideline the way a gain tolerance might be — an op-amp physically cannot produce an output voltage beyond what its supply rails provide, no matter what the resistor math says.
That’s why the calculator checks both directions independently rather than just the total supply span. A design can have a huge total swing available — 30V here, from +15V down to -15V — and still clip badly if the target output happens to sit close to one rail. Real op-amps clip a little before the literal rail voltage too, so treat the calculated headroom as an upper bound, not a value to design right up against.
When the Calculator Switches From Gain-Only to an Offset Network
R1’s value matters, but it’s the relationship between your target output, your signal, and your gain that decides which circuit topology the calculator hands you — and that decision moves the result far more than nudging any single resistor.
If your input signal times your desired gain already equals your target output, no offset is needed at all. R2 comes straight from R1 times gain minus one, and the calculator reports the input side as an open circuit, since there’s nothing to inject. Ask for a gain of exactly 1 in this mode and R2 collapses to a short — the classic unity-gain voltage follower.
When there’s a gap between your signal-scaled output and your actual target, a second voltage source fills it, and the sign of the required contribution decides where it enters the circuit. A positive contribution sums in on the non-inverting side, as in the worked example above.
A negative one — where V2 needs to pull the output down rather than up — switches to an inverting-side injection instead, and that mode requires an overall gain greater than 1 to have a feedback network to inject into at all; ask for gain at or below 1 in that situation and the calculator returns a gain error rather than a negative resistor value.
A few more conditions the code enforces directly: R1 has to be strictly greater than zero, since it sits in the denominator of the gain equation and a zero would make gain undefined. The positive supply has to be strictly greater than the negative supply, or the whole calculation is thrown out before it starts. And if an offset is required but V2 is entered as zero, there’s no source to scale, so the calculator flags it rather than dividing by zero.
Non-Inverting Op-Amp Resistor Questions
What is the formula for non-inverting op-amp gain?
Gain equals 1 plus the feedback resistor divided by the ground resistor: $Gain = 1 + R_2/R_1$. The “1” comes from the fact that the non-inverting input is buffered directly, so even with zero feedback resistance the output still tracks the input at unity gain.
How do I choose R1 and R2 for a specific gain?
Pick R1 first, generally somewhere in the low kΩ to tens-of-kΩ range to balance noise and bias current effects against loading, then solve R2 as R1 times gain minus one. Any pair with that ratio produces the same gain, so the specific R1 value is mostly a matter of practical resistor sizing rather than the math itself.
Can R1 be zero in a non-inverting amplifier?
No — R1 sits in the denominator of the gain equation, so a zero value makes gain mathematically undefined, and this calculator rejects it outright. In practice, removing R1 entirely just leaves R2 shorted from output to input, which forces unity gain rather than infinite gain.
What happens if I want a gain of exactly 1?
R2 works out to zero, meaning the output connects straight back to the inverting input with no resistor between them. That’s the standard voltage-follower configuration, used to buffer a signal without amplifying it.
Why does input bias current matter when picking R1 and R2?
Real op-amps draw a small current into each input, and if the source resistance seen by the two inputs is mismatched, that current creates a small unwanted offset voltage at the output. Matching the resistance at the non-inverting input to R1 parallel with R2 — the resistance the feedback network presents at the inverting input — cancels most of that error.
What’s the difference between inverting and non-inverting gain formulas?
Non-inverting gain is $1 + R_2/R_1$ and is always at least 1, with the output in phase with the input. Inverting gain is $-R_2/R_1$, can be less than 1, and flips the output’s polarity relative to the input.
How does supply voltage limit the maximum output swing?
The output can never exceed the positive supply rail or drop below the negative supply rail, since the op-amp has nothing to draw that extra voltage from. The usable range in practice is a little narrower than the rails themselves, since most real devices can’t swing all the way to either supply.
Can I add a DC offset to a non-inverting amplifier’s output?
Yes — a second reference voltage can be summed into the input network alongside the main signal, shifting the output by a controlled amount rather than just scaling it. Whether that offset gets added on the non-inverting or inverting side of the circuit depends on whether it needs to push the output up or pull it down relative to the signal-only result.
This calculation assumes an ideal op-amp and mathematically exact resistor values. It doesn’t account for standard resistor tolerances, finite open-loop gain and bandwidth, output current limits, or how much the input sources themselves get loaded by R3 and R4 — all of which nudge a real build slightly away from these numbers.