Estimated Input Latency

How quickly your page or app is able to respond to user input is vital to user experience. Google says through two different methods -- the RAIL performance model and Google Lighthouse -- that a site that responds longer than 50ms or 100ms is when users begin to notice a site lagging.

One thing to note: Google points out that Lighthouse only measures what is believed to be the user's perception of the response time in page load. It does not measure the actual time. In order to measure how long the real-time response is, you may need to record it in Chrome DevTools Timeline.

There are a number of ways to improve this time:

  • Offloading calculation to web workers to free up the main thread
  • Refactoring CSS selectors to perform fewer computations
  • Using CSS attributes that minimize the amount of browser-intensive procedures