Google scores every page on your website against three measured numbers. They influence where you rank, and they strongly predict whether a visitor stays or leaves. Most owners have never seen their scores, and most agencies do not volunteer them, because the mobile numbers are usually bad.
You can check them yourself for free. This article explains what you are looking at when you do.
The three numbers
LCP: how fast the page visibly loads
Largest Contentful Paint measures the time until the biggest element on screen, usually your hero image or headline, has rendered. It is the closest thing to "how long does the page take" as a user experiences it.
- Good: under 2.5 seconds
- Needs improvement: 2.5 to 4 seconds
- Poor: over 4 seconds
The usual culprits are oversized images, slow hosting, and themes that load a megabyte of scripts before showing anything.
INP: how fast the page responds to taps and clicks
Interaction to Next Paint measures the delay between a user action, like tapping a menu or a buy button, and the screen responding. A page can load fast and still feel broken if every tap takes half a second to register.
- Good: under 200 milliseconds
- Poor: over 500 milliseconds
INP problems almost always come from JavaScript: chat widgets, tracking pixels, page builders, and plugins competing for the phone's processor.
CLS: how much the page jumps around
Cumulative Layout Shift measures visual stability. You have felt this one: you go to tap a button, an ad or image loads above it, the page shifts, and you tap the wrong thing. Google measures exactly that.
- Good: under 0.1
- Poor: over 0.25
Fixes are usually mechanical: reserve space for images and embeds before they load.
Why your mobile score is the one that counts
When we audit SME websites we measure both mobile and desktop, and the gap is consistently large. A site that scores 85 on desktop routinely scores 40 on mobile. Three reasons:
- Google uses mobile-first indexing. Your mobile site is the one being ranked.
- Most of your visitors are on phones, on cellular connections, not on office fibre.
- Desktop machines hide JavaScript bloat that mid-range phones cannot.
If you only check one number, check mobile LCP. It is the most common failure and the one with the clearest revenue link: every additional second of load time measurably increases the share of visitors who leave before seeing anything.
What this has to do with AI search
Search is shifting. A growing share of queries get answered directly by AI assistants that cite a handful of sources rather than listing ten blue links. The sites that get cited are the ones that are fast, technically clean, and clearly structured, because those are the sites the crawlers can read reliably. Core Web Vitals are not just a ranking signal anymore. They are table stakes for being machine-readable at all.
Check yours today
Go to PageSpeed Insights, enter your homepage URL, and look at the mobile tab first. You will get all three numbers plus a list of suggested fixes. Two warnings from experience:
- Test your top landing pages too, not just the homepage. Product and service pages are usually heavier.
- The suggested fixes are unranked. Some are worth days of work, some change nothing. Effort and impact are different axes.
That second point is where most owners stall: the tool gives you twenty suggestions and no way to know which three matter. Prioritisation against your specific competitors is the part that takes judgment, and it is exactly what a structured audit is for.