Key takeaways
- Core Web Vitals are three measurements of real-world page experience: loading (LCP), responsiveness (INP) and visual stability (CLS).
- Google’s published “good” thresholds are an LCP of 2.5 seconds or less, an INP of 200 milliseconds or less and a CLS of 0.1 or less, measured for most real visits.
- Fast pages help visitors first and search second. Use field data, not just lab tests, to judge your site.
What Core Web Vitals are
Core Web Vitals are a small set of metrics that describe how a page feels to a real visitor. They were designed to turn vague ideas such as “fast” and “smooth” into numbers that can be tracked and improved. The set has changed over time; today it consists of three metrics.
Largest Contentful Paint (LCP): how fast the main content appears
LCP measures how long it takes for the largest visible element, usually a hero image, a big heading or a block of text, to appear. A good LCP is 2.5 seconds or less. Common causes of a poor LCP are oversized images, slow servers, render-blocking CSS and JavaScript, and web fonts that load late.
- Compress and correctly size images, and serve modern formats such as WebP.
- Use fast hosting and page caching.
- Avoid loading large scripts and styles before the main content.
Interaction to Next Paint (INP): how quickly the page responds
INP replaced the older First Input Delay metric in 2024. It looks at how long a page takes to respond visually after taps, clicks and key presses throughout the visit. A good INP is 200 milliseconds or less. Heavy JavaScript, too many third-party scripts and long tasks on the main thread are the usual culprits.
- Remove plugins and scripts you do not need.
- Delay non-essential third-party tools such as chat widgets until after the page is usable.
- Keep interactive components simple.
Cumulative Layout Shift (CLS): how stable the layout is
CLS measures unexpected movement, such as a button jumping just as you tap it because an image or ad loaded above it. A good CLS is 0.1 or less. Give images and videos explicit dimensions, reserve space for banners and embeds, and avoid inserting content above existing content.
Field data versus lab data
Lab tests, such as the ones in Lighthouse, run a page once in a controlled environment. They are excellent for finding problems. Field data comes from real visitors over time, for example in the Chrome User Experience Report and in the Core Web Vitals report in Google Search Console. Field data is what shows how your site performs for actual people on actual devices and connections, and it is what should guide priorities.
Do they affect rankings?
Google has said that page experience is one of many signals, and that great content matters more than a perfect score. The practical reason to care is simpler: slow, jumpy pages lose visitors and enquiries. Treat Core Web Vitals as a quality standard for your customers, with a possible small benefit in search.
A simple improvement plan
- Measure: check Search Console and PageSpeed Insights for your key pages on mobile.
- Fix the biggest image and script problems first, since they usually deliver most of the gain.
- Re-test after changes, and watch field data over the following weeks.
Speed is built in from the start when we design and develop websites, and we can also audit an existing site: get in touch.
Frequently asked questions
What is a good LCP score?
Google considers an LCP of 2.5 seconds or less to be good, measured for the majority of real visits.
What replaced First Input Delay?
Interaction to Next Paint (INP) replaced First Input Delay as a Core Web Vital in 2024. It measures responsiveness across the whole visit rather than just the first interaction.
Where can I see my Core Web Vitals?
In the Core Web Vitals report in Google Search Console, in PageSpeed Insights (which shows field data when available) and in Lighthouse for lab testing.
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