Three metrics
Each metric stands for loading, responsiveness or visual stability (Walton, 2020). LCP (Largest Contentful Paint) should be within 2.5 seconds. INP (Interaction to Next Paint), which replaced FID in 2024, should be 200 ms or less. CLS (Cumulative Layout Shift) should be 0.1 or less. All are judged at the 75th percentile of real users rather than in the lab.
Rooted in response-time research
Miller (1968) observed that responses under 0.1 seconds feel instantaneous while several seconds break the flow, and Nielsen (1993) popularised the 0.1, 1 and 10 second limits. Nah (2004) found tolerable waits without feedback of about two seconds; Galletta et al. (2004) showed delays reduce attitudes and return intentions; and Arapakis et al. (2014) showed users notice differences of a few hundred milliseconds.
Perceived speed and limits
Bouch et al. (2000) found incrementally rendered pages feel faster, the idea behind LCP and skeleton screens. Core Web Vitals are one ranking signal, linking them to search engine optimisation, but they do not outweigh relevance. Chasing numbers alone risks Goodhart's law. In markets with slow networks and budget phones, mobile-first design pays off most.
FAQ
- What are the Core Web Vitals thresholds?
- LCP 2.5 s or less, INP 200 ms or less and CLS 0.1 or less, met by at least 75% of real visits.
- Do good scores raise search rankings?
- They are a signal but a modest one; relevance and quality come first, and vitals can break ties.
Sources reviewed: 2026-10-27
References
- Miller, R. B. (1968). Response time in man-computer conversational transactions. In Proceedings of the December 9–11, 1968, Fall Joint Computer Conference, Part I (pp. 267–277). ACM. The classic behind the 0.1 s, 1 s and 10 s response-time thresholds that inform INP.
- Nah, F. F.-H. (2004). A study on tolerable waiting time: How long are Web users willing to wait? Behaviour & Information Technology, 23(3), 153–163. Experiments on how long web users will wait, useful for setting load-time goals.
- Galletta, D. F., Henry, R., McCoy, S., & Polak, P. (2004). Web site delays: How tolerant are users? Journal of the Association for Information Systems, 5(1), 1–28. Shows delays lower attitudes and return intentions, the business impact of speed.
- Bouch, A., Kuchinsky, A., & Bhatti, N. (2000). Quality is in the eye of the beholder: Meeting users' requirements for Internet quality of service. In Proceedings of the SIGCHI Conference on Human Factors in Computing Systems (pp. 297–304). ACM. Finds incrementally rendered pages feel faster, relevant to LCP and perceived speed.
- Arapakis, I., Bai, X., & Cambazoglu, B. B. (2014). Impact of response latency on user behavior in web search. In Proceedings of the 37th International ACM SIGIR Conference on Research and Development in Information Retrieval (pp. 103–112). ACM. Shows users notice and react to delays of a few hundred milliseconds.
- Walton, P. (2020). Web Vitals. web.dev. The official definitions and 'good' thresholds for LCP, CLS and INP.
- Nielsen, J. (1993). Usability engineering. Academic Press. A classic framing response-time limits as part of usability.