Core Web Vitals in plain English

What the three Core Web Vitals actually measure

Google needed a way to judge whether a page is annoying to use, so it settled on three things it can measure automatically.

• Largest Contentful Paint. How long until the biggest thing on screen, usually your hero image or heading, has actually appeared. Aim for under 2.5 seconds.
• Interaction to Next Paint. When somebody taps or clicks, how long before the page visibly responds. Aim for under 200 milliseconds.
• Cumulative Layout Shift. How much the page jumps about while loading. Everyone has tried to tap a button and had an advert push it out of the way. Aim for under 0.1.

That is genuinely all they are. Loading, responsiveness, and whether things move around.

How much they really matter for rankings

Honestly? Less than the people selling speed optimisation would like you to think, and more than nothing.

Google has been clear that page experience is a tie breaker. If two pages answer the question equally well, the faster and more stable one wins. If your content is thin and nobody links to you, a perfect score will not save it.

The stronger argument for fixing them has nothing to do with rankings. People leave slow sites. On mobile, every extra second measurably costs you enquiries, and that happens whether or not Google ever notices.

How to measure them properly

There are two kinds of data and people confuse them constantly.

Lab data is a simulated test run on demand, like the score PageSpeed Insights gives you at the top. Useful for diagnosis, easy to game, and not what Google ranks on.

Field data is what real visitors actually experienced over the last 28 days. That is what counts. In PageSpeed Insights it is the section headed with real user experience, and in Search Console it is the Core Web Vitals report.

Two rules. Always look at the mobile numbers, because that is where most of your traffic is and where the scores are worst. And never judge the site on the home page alone, because your service pages are usually the ones people land on.

The fixes that are actually worth it

In our experience the same handful of problems account for most failures on small business sites, and they are not exotic.

• Oversized images. By far the biggest cause. A photo uploaded straight from a phone can be several megabytes where it needs to be a hundred kilobytes. Resize to the size it displays at and serve modern formats.
• Missing width and height on images. This is what causes most layout shift, and it is a five minute fix.
• Too many plugins. Every one adds scripts to every page, including the pages that do not use it.
• Sliders and carousels in the hero. Almost always the single heaviest thing on the page, and they rarely earn their keep.
• Fonts loading late. Causes text to flash or shift. Preload the ones you need and drop the ones you do not.
• Cheap hosting. If the server takes 800 milliseconds to respond, nothing you do on the page recovers that.

What is usually not worth paying for

Some speed work is expensive, fragile and barely moves the number that matters.

• Chasing a perfect lab score when field data already passes
• Aggressive script deferral that breaks forms, maps or booking tools
• Rebuilding a working site purely for speed, when images and hosting were the problem
• Optimisation plugins stacked on top of each other, which frequently conflict

A sensible target is passing on mobile field data. Beyond that the returns fall away sharply.

Where to start on Monday

If you do nothing else, do these in this order.

• Run your three most important pages through PageSpeed Insights on mobile and write down the field data
• Find the largest image on each page and resize it properly
• Check every image has width and height set
• Deactivate any plugin you cannot name the purpose of
• Re test in a fortnight, because field data lags by 28 days

That list alone fixes the majority of small business sites we are asked to look at.

Michael James

Michael heads up NE1 Web Design & SEO in North Shields and has been building websites for more than twenty years.