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How fast a website loads is the first thing that decides whether a visitor stays. Google measures user experience with three metrics it calls Core Web Vitals and considers them among its page experience signals. The good news: these metrics are measurable and can often be improved significantly with a few targeted changes.
#What are Core Web Vitals?
| Metric | What it measures | Good | Poor |
|---|---|---|---|
| LCP (Largest Contentful Paint) | When the largest content element becomes visible | ≤ 2.5 s | > 4 s |
| INP (Interaction to Next Paint) | How quickly the page responds to clicks and taps | ≤ 200 ms | > 500 ms |
| CLS (Cumulative Layout Shift) | How much content shifts while the page loads | ≤ 0.1 | > 0.25 |
INP replaced the older FID (First Input Delay) metric in March 2024. Assessment is based on the 75th percentile of real-user data — the goal is a good experience for the large majority of visitors.
#Why speed matters so much
- Visitor behaviour: Slow pages get abandoned, especially on mobile connections.
- Conversions: Every delay in forms and checkout steps is a potential lost customer.
- Search engines: Page experience is one of the signals Google considers when ranking.
- Cost: Lightweight pages use fewer server resources and less bandwidth.
#How to measure website speed
There are two kinds of data. Lab data (tools such as Lighthouse) measures a single load in a controlled environment and is ideal for finding problems. Field data is collected from real users — and it is what Google uses in its assessment.
- PageSpeed Insights: Shows field and lab data on one screen.
- Google Search Console → Core Web Vitals report: Monitors all your pages in groups.
- Chrome developer tools: Find the source of a problem with the Lighthouse and Performance panels.
#How to improve LCP
- Compress the main image and serve it in modern formats such as WebP/AVIF at the right size for the screen.
- Don't lazy-load the image at the top of the page; load it with priority.
- Reduce server response time: caching, static page generation and servers close to your users.
- Load only the font weights you use and use
font-display: swap.
#How to improve INP
- Remove unused JavaScript and question every third-party script (chat, analytics, ads).
- Split long tasks so the main thread isn't blocked for long.
- Load heavy components only when they are needed.
#How to improve CLS
- Give images and videos a width and height so the browser can reserve space.
- Reserve space for banners, ads and cookie notices that load later.
- Prevent web fonts from shifting text while they load.
#Is speed alone enough?
No. Speed is a prerequisite for a good user experience, but content quality and fit with search intent decide rankings. The best results come from fast infrastructure, correct technical SEO and content that genuinely answers the user's question — together.
To measure where your site stands and get a prioritised improvement plan, see our SEO and performance optimisation service.
Frequently asked questions
How much do Core Web Vitals affect rankings?
They are one page experience signal; they don't replace content quality, but can make a difference between pages of similar quality and directly affect visitor behaviour.
Does my PageSpeed score need to be 100?
No. The real goal is for all three metrics to be in the “good” range in real-user data. The lab score is a guide for finding problems.
Why do mobile and desktop results differ?
Mobile tests simulate a slower processor and connection. Since most visitors arrive on mobile, mobile results should be the priority.