Op-amp buffer follower calculator
Put 2.5 V on the non-inverting input of an op-amp follower and 2.5 V comes out: a gain of one and no inversion. Enter the input voltage to confirm the ideal buffer output and see why it barely loads its source. Free in your browser.
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Worked example
- Input voltage
- 2.5
- Output voltage
- 2.5
- Voltage gain
- 1
- Configuration
- voltage_follower
- Input impedance
- very high (ideally infinite)
This op-amp buffer follower calculator evaluates the ideal voltage-follower connection in one step. Enter the voltage applied to the non-inverting input and it confirms a closed-loop gain of one, copies that voltage to the output, and reports that the signal is not inverted. It also explains the defining buffer behavior: very high input impedance and very low output impedance. That combination lets one circuit stage observe a signal without heavily loading its source while driving the following stage more effectively. The calculation is deterministic and runs without a network connection, random values, or time-dependent data. It is an ideal first-pass result, so practical output swing, current, bandwidth, offset, slew rate, and stability limits still depend on the selected op-amp and its power supplies.
Why a voltage follower has unity gain
A voltage follower is the simplest closed-loop operational-amplifier configuration. The source drives the non-inverting input, and the output connects directly to the inverting input. That connection feeds the complete output signal back with negative feedback.
In the ideal linear model, the op-amp changes its output until the voltage difference between its two inputs is zero. The inverting input therefore sits at the output voltage, the non-inverting input sits at the entered source voltage, and those values must be equal. Written as a transfer relationship, Vout equals Vin and the closed-loop voltage gain Av equals Vout divided by Vin, which is one wherever the ratio is meaningful.
The calculator reports unity gain explicitly even when the entered voltage is zero, where directly dividing zero by zero would be indeterminate; topology, rather than numerical division, establishes the gain. Positive input values remain positive, and negative values remain negative, so there is no phase inversion. Unlike a resistor-set non-inverting amplifier, a follower does not ask for Rf and Rg because its output-to-inverting-input connection fixes the feedback factor at one.
The result is a buffer, not a voltage amplifier: it reproduces voltage while changing the impedance seen by the surrounding stages. This ideal equality assumes negative feedback is operating normally and the device remains inside its linear region. A real output cannot necessarily equal an input beyond its allowed common-mode range or output swing, but those device-specific boundaries require a datasheet and supply information that are intentionally outside this focused calculation.
How to read the output and impedance report
Numbers may represent volts, millivolts, or another consistent voltage unit because multiplication by one does not change scale; the returned output uses exactly the same unit implied by the input. Do not append a unit symbol inside the numeric field. The impedance strings describe the standard ideal model.
Very high input impedance means the op-amp input draws essentially no current, so the follower places little load on a high-resistance sensor, divider, or preceding filter. Very low output impedance means feedback makes the output behave more like a stiff voltage source for the next stage. Ideal analysis takes those limits to infinite input impedance and zero output impedance, but the response deliberately uses qualitative wording because real impedances are neither universal nor exactly infinite or zero.
Their numeric values vary with device, frequency, feedback, load, temperature, and operating point. Use the chosen op-amp datasheet or a circuit simulation when actual bias current, input capacitance, closed-loop output impedance, or frequency dependence matters.
Practical checks and real-world limitations
Use the result as an ideal topology check before selecting a physical component. If the input is negative 0.75, the ideal output remains negative 0.75 because a follower is non-inverting. Then compare the ideal result with the op-amp datasheet.
Verify that the input common-mode range includes the requested voltage at the planned supply rails, and that the guaranteed output swing reaches it under the expected load. Check output-current capability because low output impedance does not mean unlimited current. Review gain-bandwidth and slew-rate requirements for changing signals, input offset and bias current for precision sources, noise for low-level measurements, and capacitive-load guidance for stability.
Some op-amps are not unity-gain stable; using one as a follower can oscillate even though the DC equation is correct. Rail-to-rail labels also require care because performance near either rail depends on supply voltage, load, temperature, and the exact device. This calculator intentionally does not clip the output to unspecified rails or invent impedance values without a part number.
If the ideal output appears impossible for the hardware, treat that discrepancy as a design warning and continue with datasheet limits or SPICE. The follower’s central purpose remains impedance transformation: isolate a source from a load while ideally preserving the same instantaneous voltage and polarity between input and output.
What you can do with it
Sensor signal buffering
Confirm the ideal voltage delivered by a follower that isolates a high-impedance sensor from an ADC or downstream network.
Schematic and homework checks
Verify that direct output feedback creates a non-inverting unity-gain stage and document the expected output for a given input.
FAQ
What is the voltage gain of an op-amp follower?
The ideal closed-loop voltage gain is exactly one, so Vout = Vin and the signal polarity is unchanged.
Why use a follower if it does not amplify voltage?
It buffers stages: its very high input impedance minimizes source loading, while its very low output impedance improves load-driving behavior.
Are the input and output impedances really infinite and zero?
No real op-amp reaches those ideal limits. Actual values depend on the device, feedback, frequency, load, and operating conditions.
Does this calculator account for supply-rail clipping?
No. It returns the ideal linear result. Check common-mode range and output-swing specifications for the chosen op-amp and supplies.
Can every op-amp be connected as a voltage follower?
No. The device must be stable at unity gain, and its voltage, current, bandwidth, slew-rate, and load limits must suit the circuit.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/elec/opamp-follower \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"input_voltage":2.5}'const res = await fetch("https://api.kit.forhosting.com/elec/opamp-follower", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"input_voltage": 2.5
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/elec/opamp-follower",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"input_voltage": 2.5
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/elec/opamp-follower", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"input_voltage":2.5}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"input_voltage":2.5}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/elec/opamp-follower", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"input_voltage": 2.5
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "elec.opamp_follower",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_abs_voltage | 1000000000000 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
How to read the output and impedance report
Provide input_voltage as a finite number, or use the accepted vin, v_in, or input aliases. The response echoes input_voltage, returns the identical output_voltage, sets voltage_gain to one, and sets unity_gain_confirmed to true. It also identifies the configuration as voltage_follower, reports no phase inversion, gives the formula Vout equals Vin, and includes short calculation steps. Invalid, missing, non-finite, or out-of-range inputs return invalid_input rather than producing misleading JSON. A successful API request costs $0.002, while the browser calculation uses the same pure solve function locally.
Practical checks and real-world limitations
If input_voltage is 2.5, output_voltage should be 2.5 and voltage_gain should be one.
Integration use cases
Bench-test fixtures
Generate deterministic expected values for follower tests before comparing measurements against real offset, swing, and loading effects.