What is input lag and why does it matter?

Input lag is the delay between an action happening — a button press, a mouse click, a game state change — and that change becoming visible on screen. For competitive gaming and any latency-sensitive interaction, lower input lag means the on-screen result feels more directly tied to your action. It's made up of several stages: input device latency, system processing, and display processing.

Why does this test's result vary so much between trials?

Human reaction time itself varies by a wide margin from trial to trial — typically 150–300ms — and that variability is far larger than any latency this browser test can detect. Run enough trials to get a stable median rather than trusting any single result.

Can a browser-based test measure true monitor input lag?

Not precisely. Lab-accurate monitor input lag measurement uses a photodiode timer that detects the exact moment a pixel changes and compares it against the exact moment the source signal changed — a level of precision a click-based reaction test can't reach, since it's dominated by human reaction time. This test is best used for relative before/after comparisons, not as a substitute for a manufacturer's rated or independently lab-tested input lag figure.

What is the difference between input lag and pixel response time?

Input lag is about timing — how long before an action's effect appears on screen at all. Pixel response time is about the transition itself — how long an individual pixel takes to change from one color to another once the panel starts drawing the new frame. A monitor can have low input lag but slow pixel response (visible smearing on fast motion), or the reverse.

Does a wireless mouse or keyboard add noticeable input lag?

It can. Wireless input devices, especially older Bluetooth ones or those with a low polling rate, add their own latency on top of whatever the display contributes. A wired connection or a wireless device with a high, stable polling rate (many gaming-focused wireless mice now match wired performance) minimizes this layer.

How can I reduce latency in my overall setup?

Disable any motion-smoothing, video-processing, or 'game mode' toggles in your monitor's OSD that aren't already optimized for low latency — many enhancement features trade added processing delay for picture quality. Use a wired connection where possible, close background applications competing for CPU time, and keep GPU drivers current.

Input Lag Test

The Input Lag Test has you click Start Trial, wait for the box to flip green, then click it as fast as you can — timing the gap with performance.now() across several trials and reporting your median and range. Run it more than once, since a single click can be thrown off by a slow reaction, and keep in mind this measures your browser, operating system, and compositor stacked together with your own reflexes — not your display panel's true input lag, which only specialized hardware can isolate. Use the ips glow test to confirm whether your monitor shows this issue before you adjust settings or return it.

Input Lag Test

Click Start Trial, then click or tap the box the instant it turns green. Run several trials — a single click can be thrown off by a slow reaction.

Click Start Trial

Run a few trials to see your median and spread.

Click Start Trial, wait for the box to turn green, then click it as fast as you can. This measures the round trip from the moment your browser paints the green cue to the moment it registers your click — your reaction time and browser/system latency combined, not a lab-grade measurement of your monitor's own signal-processing lag.

What This Test Actually Measures

True monitor input lag — the delay a display's own scaler and processing pipeline add between receiving a signal and putting light on the panel — is typically a handful of milliseconds on a modern gaming monitor, and measuring it properly requires dedicated hardware: a photodiode timer that detects the exact moment a pixel changes, compared against the exact moment the source signal changed. A browser-based click test can't isolate that number, because it's dominated by a much bigger and much less consistent factor: human visual reaction time, which typically runs 150–300ms even for an alert person paying full attention. The black level test works on any screen — laptop, external monitor, or TV — with nothing to install.

What this test is good for is relative comparison — running it before and after a setup change (switching cables, disabling a game-mode processing feature in your monitor's OSD, changing browsers) and comparing the median across many trials. Because reaction time swamps any monitor-side difference, don't read a single trial's number, or even one session's median, as a precise latency spec — use it to spot large, repeatable shifts, not to benchmark your display against a manufacturer's rated input lag figure.

Why Median and Range, Not a Single Number

Human reaction time varies substantially from trial to trial even under identical conditions — attention lapses, anticipation, and simple motor variability all add noise. Averaging is misleading here because a handful of unusually slow trials (you got distracted, you weren't looking at the box) can drag a mean far off from your typical performance. The median is far more robust to those outliers, and the range shown alongside it tells you how consistent your trials were — a tight range means the number is trustworthy; a wide range means run more trials before drawing any conclusion. Run the clouding test for a few seconds under normal room lighting for the most reliable result.

The random delay before each cue (0.8–2.6 seconds) is deliberate — it prevents you from timing your click to a predictable interval instead of genuinely reacting to the color change, which would measure your sense of rhythm rather than actual response latency.

Sources of Latency Between the Cue and Your Click

Even setting aside human reaction time, several layers sit between "the browser decided to paint green" and "the browser registered your click," and each can add a small, variable amount of delay:

Display refresh timing — the cue can only actually appear on the next refresh interval the panel presents, so a lower refresh rate adds a small, fixed ceiling to how fast the change can become visible at all.
Input device latency — wireless mice and keyboards, and devices with a low polling rate, add their own delay between the physical click and the OS receiving it, on top of whatever the display side contributes.
System load — background processes competing for CPU time can delay both the paint and the event-handling side of the round trip.
Browser and OS input handling — different browsers and operating systems have measurably different input-to-paint pipelines, which is part of why comparing across browsers rather than only within one can be informative.

None of these individually add more than a few milliseconds under normal conditions, but a change that noticeably shifts your median across many trials — a cable swap, a driver update, disabling a monitor's video-processing feature — is worth taking seriously even though this test can't tell you exactly which layer improved.

Frequently Asked Questions

What is input lag and why does it matter?: Input lag is the delay between an action happening — a button press, a mouse click, a game state change — and that change becoming visible on screen. For competitive gaming and any latency-sensitive interaction, lower input lag means the on-screen result feels more directly tied to your action. It's made up of several stages: input device latency, system processing, and display processing.
Why does this test's result vary so much between trials?: Human reaction time itself varies by a wide margin from trial to trial — typically 150–300ms — and that variability is far larger than any latency this browser test can detect. Run enough trials to get a stable median rather than trusting any single result.
Can a browser-based test measure true monitor input lag?: Not precisely. Lab-accurate monitor input lag measurement uses a photodiode timer that detects the exact moment a pixel changes and compares it against the exact moment the source signal changed — a level of precision a click-based reaction test can't reach, since it's dominated by human reaction time. This test is best used for relative before/after comparisons, not as a substitute for a manufacturer's rated or independently lab-tested input lag figure.
What is the difference between input lag and pixel response time?: Input lag is about timing — how long before an action's effect appears on screen at all. Pixel response time is about the transition itself — how long an individual pixel takes to change from one color to another once the panel starts drawing the new frame. A monitor can have low input lag but slow pixel response (visible smearing on fast motion), or the reverse.
Does a wireless mouse or keyboard add noticeable input lag?: It can. Wireless input devices, especially older Bluetooth ones or those with a low polling rate, add their own latency on top of whatever the display contributes. A wired connection or a wireless device with a high, stable polling rate (many gaming-focused wireless mice now match wired performance) minimizes this layer.
How can I reduce latency in my overall setup?: Disable any motion-smoothing, video-processing, or 'game mode' toggles in your monitor's OSD that aren't already optimized for low latency — many enhancement features trade added processing delay for picture quality. Use a wired connection where possible, close background applications competing for CPU time, and keep GPU drivers current.