Core Web Vitals

Example

The owner of an online garden-tools shop gets an email from Google Search Console saying the shop’s mobile pages have an LCP problem. The phone report shows three numbers: LCP 3.4 seconds, INP 180 milliseconds, CLS 0.05. Two of the three are good, yet the page fails the assessment, because Google only passes a page when all three are. LCP has to come down by 0.9 seconds, and that time almost always sits in the large photo or slider at the top of the page, not in the site as a whole.

The thresholds the report is read against:

• LCP — when the largest visible element appears: good at 2.5 s or less, poor above 4 s.
• INP — how fast the page reacts to a click, tap or key press: good at 200 ms or less, poor above 500 ms.
• CLS — how much the layout moves while the page loads: good at 0.1 or less, poor above 0.25.

Anything between the two thresholds is marked as needing improvement.

Why it matters for a business

Google does use Core Web Vitals in ranking, but lightly: between two equally useful pages the faster one gets the edge, while a slower page with a better answer still outranks a fast, thin one. The difference shows up first in orders and enquiries. A visitor staring at a blank screen, or tapping a button that has just jumped, leaves, and with paid traffic that visitor is a click you have already paid for. Slow pages lose people before they reach the offer, and it shows directly in your conversion rate.

What to ask

• Are the numbers from real visitors or from a single lab test? Google judges on the first.
• Phone or desktop? They are assessed separately, and mobile is almost always the weaker one.
• Which metric fails, and on which pages? LCP on category pages is different work from INP in the basket.
• When will the result show? The data covers 28 days, so the report catches up about a month after the fix.

In our website speed optimisation work we record all three metrics before we start and compare them on the same instrument afterwards.