Core Web Vitals: the details
Each has a “good” threshold: LCP of 2.5 seconds or less, INP of 200 milliseconds or less and CLS of 0.1 or less. They are assessed with data from real Chrome users at the 75th percentile: three out of four visits have to pass. INP replaced FID in March 2024 and is more demanding, because it measures every interaction in the visit and not just the first.
They are part of the page experience signals Google uses for ranking, though with less weight than content relevance. Their clearest effect is on the business: a slow page loses visitors before it shows anything. The usual causes of a poor result are images without dimensions, fonts that block first paint, too much JavaScript and content inserted late.