Pixel response time
Pixel response time measures how long a pixel takes to change from one color to another. Advertised as gray-to-gray (GTG) or black-to-white (BTW) in milliseconds.
What it affects: Motion clarity. A slow pixel lingers at an intermediate value during a transition, leaving a ghostly trail behind moving objects. Fast response times mean sharp, clear motion.
Typical values:
The catch: Manufacturers measure GTG from gray to gray, selecting the transition that looks best. The industry-standard test is from 80% gray to 20% gray - often not the worst case on VA panels. Independent review sites measure all gray transitions and report the worst case, which can be much higher.
Input lag
Input lag measures the time between a physical action (moving a mouse, pressing a button) and the result appearing on screen. This includes:
Measured in milliseconds at the display pipeline boundary.
What it affects: How responsive the game feels. High input lag makes games feel sluggish and rubber-banded regardless of how smooth the motion looks.
Typical display processing latency (monitor's own contribution):
Why you can have one without the other
A monitor with fast pixel response time but poor signal processing will have sharp motion but sluggish controls. A monitor with low input lag but slow pixels will feel responsive but motion will be blurry.
Both matter. Great gaming monitors optimize for both - OLED panels are currently the best at both simultaneously.
Testing
The Reaction Time test on this site measures your total reaction time loop including monitor output lag (light from the screen) and human response. Using it consistently on the same monitor lets you track improvement. Using it across different monitors reveals relative latency differences.