Core Web Vitals Explained for Business Owners
Updated · Vanta Foundry
Short answer
What are Core Web Vitals, and do they matter for my website?
Core Web Vitals are three measurements Google uses to describe how a page feels to real visitors: Largest Contentful Paint (how fast the main content appears), Interaction to Next Paint (how fast the page responds to a tap or click) and Cumulative Layout Shift (how much the page jumps while loading). Google's guidance at web.dev calls a page good at 2.5 seconds or less for LCP, 200 milliseconds or less for INP and 0.1 or less for CLS, measured at the 75th percentile of visits on mobile and desktop separately.
The Three Measurements
Each is judged at the 75th percentile: at least three in four visits should meet the threshold, counted separately for phones and computers. These definitions are Google's, published at web.dev.
- Largest Contentful Paint (LCP): the time until the biggest image or block of text in view has loaded. Good is 2.5 seconds or less.
- Interaction to Next Paint (INP): how long the page takes to visibly respond after a tap, click or key press, across the visit. Good is 200 milliseconds or less. INP replaced First Input Delay as a Core Web Vital in 2024.
- Cumulative Layout Shift (CLS): how much content moves around unexpectedly while the page loads, such as a button jumping as an image arrives. Good is 0.1 or less.
Lab Scores and Real Visitors
A lab test such as Lighthouse loads the page once on a simulated device. It is useful for finding problems, but it isn't what Google reports for your site. The field data in Search Console and PageSpeed Insights comes from real Chrome visitors over the previous 28 days, and a page with little traffic may have no field data at all.
So a perfect lab score doesn't guarantee good field numbers, and a weak lab score on a fast connection may still pass in the field. Check both, and trust the field data when you have it.
What Usually Fixes Each One
- Slow LCP: an oversized hero image, a slow server response, or text waiting on a web font. Serve correctly sized, modern-format images, cache pages close to visitors, and load the main image first.
- Slow INP: too much JavaScript running when someone taps. Ship less script to the browser, break up long tasks, and load chat widgets and trackers after the page is usable.
- High CLS: images, embeds or banners without reserved space. Give every image and embed its dimensions, and don't insert content above what the visitor is reading.
How Much They Matter
Core Web Vitals are one of many signals Google uses; relevant, useful content matters more. Their bigger effect is on people: a page that appears quickly and doesn't jump keeps more visitors reading and buying. Nobody can promise a ranking from better scores.
Checking Your Own Site
Every site we build is tested for speed before launch: see website development. If an existing site is slow, a redesign or migration may fix it, or a targeted repair may be enough.
- Search Console, Core Web Vitals report: field data grouped by page type.
- PageSpeed Insights: field data for one URL plus a lab test with suggestions.
- Test on a real mid-range phone on mobile data, not only on a fast laptop.
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