Input lag is the delay between moving your mouse and seeing the result on screen. Everyone chases lower latency, but few people actually measure it, which makes it easy to spend money on gear that changes nothing. Measuring the full click-to-photon chain tells you whether your bottleneck is the display, the render queue, or the game engine, and it turns “this feels laggy” into a number you can improve.
The three latencies people confuse
System latency is the whole pipeline: mouse polling, CPU processing, GPU render, and display scan-out. Display response time (measured in milliseconds gray-to-gray) is only the last link. Network ping matters online but is separate from local input lag. When someone says a monitor “feels laggy,” the cause is often render-queue latency, not the panel, which is why buying a faster monitor sometimes changes nothing.
Rough contributions to total latency
| Stage | Typical range | Biggest lever |
|---|---|---|
| Mouse polling | 1–8 ms | 1000 Hz+ polling rate |
| Render queue / CPU | 5–40 ms | Reflex, frame cap, higher fps |
| GPU render | 3–20 ms | Lower settings, higher fps |
| Display scan-out | 2–16 ms | Higher refresh rate |
Method 1: software measurement
Overlays that expose render and PC latency give you a number without extra hardware. Enable the latency readout in your GPU vendor’s overlay or a frame-time tool, run a fixed scene, and record the average PC latency in milliseconds. This captures everything up to the point the frame leaves the GPU. It will not include the monitor’s own scan-out delay, but it is perfect for comparing settings, because the monitor stays constant between tests.
What to test
- Lock a baseline: same map, same resolution, vsync off.
- Record PC latency with settings at your normal preset.
- Toggle one variable, such as a frame cap 3–5 fps below your refresh rate, and re-record.
- Note the change. A good uncapped-to-capped move can shave 10–30 ms on a GPU-bound scene.
Method 2: the high-speed camera trick
To capture true click-to-photon latency including the panel, film your mouse and screen together at 240 fps or higher, which most modern phones can do. Each frame at 240 fps is about 4.2 ms. Count the frames between the mouse button visibly pressing and the on-screen muzzle flash or crosshair reaction, then multiply by the per-frame time. Averaging ten clicks gives a reliable figure and needs zero paid tools. Use a well-lit room so the exact frame of the click is easy to spot.
Turning numbers into wins
Once you can measure, the priorities become obvious. Raising frame rate is the single largest lever because latency scales roughly with frame time; going from 60 to 120 fps often halves the render portion. A frame cap that keeps the GPU below 97% usage prevents the render queue from filling. Enabling a low-latency mode paired with that cap is nearly free. Only after those should you consider a faster panel, which typically trims the smallest slice of the pipeline.
Beware placebo
Latency changes of a few milliseconds are hard to feel reliably, and expectation strongly colors perception. That is exactly why measurement matters: a blind test with recorded numbers keeps you honest and stops you from “feeling” improvements a change did not actually produce. If two settings measure within 2–3 ms of each other, treat them as equal and choose the one with better image quality or higher frame rate.
FAQ
Does higher fps reduce input lag even above my refresh rate?
Yes, up to a point. Rendering more frames than the display shows still lowers the age of the most recent frame, which trims a few milliseconds. That is why competitive players sometimes uncap fps and accept tearing, or use a low-latency mode with a cap just under refresh.
Is 240 fps phone video accurate enough?
For hobby testing, yes. At 4.2 ms per frame the margin of error over a ten-click average is small compared to the differences you are trying to detect, which are usually 10 ms or more.
Bottom line
You cannot optimize what you cannot see. Use an in-game latency overlay for fast, repeatable settings comparisons, and a 240 fps camera when you want the true click-to-photon number that includes the monitor. Chase frame rate and a smart frame cap first; they deliver the biggest latency reductions before you spend a cent on new hardware, and measured numbers keep you from paying for placebo.
