Core Web Vitals for store owners: what Google actually measures

Core Web Vitals are three numbers Google collects from real visitors to your store. They affect your search ranking, but more importantly they describe the experience that decides whether a visitor stays or leaves.

The three numbers

LCP — Largest Contentful Paint. How long until the biggest thing on the screen (usually your hero or product image) is visible. Good is under 2.5 seconds. A slow LCP means visitors stare at a blank or half-painted page.

INP — Interaction to Next Paint. When a visitor taps “Add to cart”, how long before the page visibly responds. Good is under 200ms. A bad INP makes your store feel broken — people tap the button twice, then leave.

CLS — Cumulative Layout Shift. How much the page jumps around while loading. Good is under 0.1. Layout shift is why customers tap “Buy now” and hit a cookie banner instead.

Check yours in two minutes

Go to PageSpeed Insights, enter your homepage URL, and read the top section labeled “Discover what your real users are experiencing” — that’s field data from actual visitors, not a simulation. Then test your best-selling product page, because that’s where the money is and it’s usually heavier than the homepage.

What to do with the result

If only LCP is red, you have an image or server problem — usually a fixable afternoon of work. If INP is red, some script is hogging the main thread; on WooCommerce stores it’s typically a poorly-built plugin. If CLS is red, something loads late and pushes content down — banners, embeds, or images without declared dimensions.

One red metric is a project. Three red metrics is a hosting-and-theme conversation. Either way, you now know more than most agencies will tell you.