Site speed, and the numbers Google measures

The three numbers that matter

Google groups its speed measurements under the name Core Web Vitals. There are three, and each corresponds to something a real person actually notices.

• LCP — Largest Contentful PaintHow long until the main thing on screen appears. Usually your headline or hero image. Google wants this under 2.5 seconds. This is the one that matters most.
• CLS — Cumulative Layout ShiftHow much the page jumps around while loading. If you have ever gone to tap a button and something loaded above it, pushing it down so you tapped the wrong thing — that is CLS. Should be under 0.1.
• INP — Interaction to Next PaintHow quickly the page responds when you tap or click. A menu that takes half a second to open feels broken even though it works. Should be under 200 milliseconds.

Why slow sites lose money twice

The first loss is obvious. People do not wait. Someone on a phone with a weak signal will give you a couple of seconds before backing out, and they will not try again later.

The second loss is less obvious and often larger. Google uses page experience, including these speed measurements, as part of how it ranks pages. A slow site sits lower in results, so fewer people ever see it. You are not just losing a share of your visitors — you are losing a share of the people who would have become visitors.

This compounds with the technical SEO basics. A site that is slow and hard to crawl is fighting on two fronts.

What actually makes small business sites slow

In practice the causes are boringly consistent. It is almost always one or more of these five.

• Enormous imagesBy far the most common. A photo straight off a phone can be 5MB where it needs to be perhaps 150KB. Sites regularly carry ten times more image weight than necessary, and it is invisible on a fast office connection — images and media covers the fix.
• Too many pluginsEvery plugin adds code to every page, including pages that do not use it. A site with forty plugins is loading forty sets of scripts to render a page about your opening hours.
• Bloated themesMultipurpose themes ship with code for every feature they could possibly offer — sliders, shops, booking systems, portfolios — and load a good deal of it whether you use it or not.
• No cachingWithout caching, the server rebuilds the entire page from scratch for every single visitor. Caching means it builds it once and hands out copies. This is often a single setting nobody switched on.
• Third-party scriptsChat widgets, analytics, tracking pixels, review embeds, font services. Each one is a request to someone else's server, and your page waits for them. Four or five of these will visibly slow a site.

What to do about it

Roughly in order of how much difference they make relative to effort: compress and correctly size every image; remove plugins you do not use; turn on caching; audit third-party scripts and delete the ones nobody looks at; and only then consider changing theme or rebuilding.

That order matters. People often jump straight to "we need a new website" when resizing the images would have got them most of the way for a fraction of the cost.

Speed also interacts with layout. A page that loads fast but jumps around as it does so still feels broken — see responsive design for why that happens most on phones.

Sources and further reading

• Core Web Vitals (opens in a new tab)Google web.devThe definitive explanation of LCP, CLS and INP.
• PageSpeed Insights (opens in a new tab)GoogleFree. Test any page in under a minute.
• Understanding page experience (opens in a new tab)Google Search CentralHow speed factors into ranking, from Google directly.

Common questions

How fast should my website be?

Aim for the main content appearing within 2.5 seconds on a mobile connection. Under one second is achievable for most small business sites and feels instant. If you are currently at six or seven seconds, which is common, the first round of fixes usually gets you most of the way.

Does site speed really affect Google rankings?

Yes, though it is one signal among many. Relevance and content still matter more. Think of speed as a tiebreaker: between two similarly relevant pages, the faster one wins. When you are competing locally against a handful of similar businesses, tiebreakers decide it.

My site is fast on my computer. Why does the test say it is slow?

Because you are testing on a fast connection, on a good device, with the site already cached in your browser. Testing tools simulate a mid-range phone on mobile data, which is much closer to your actual visitors. Your own experience of your site is the least reliable measurement available.