Why phones are different
A phone has a slower processor than a laptop and often a slower, less steady connection. Large images, heavy scripts and web fonts that a laptop shrugs off can hold a phone up for seconds. Google also judges most sites by how they behave on phones, so a slow mobile site can cost you visitors and rankings.
What Google measures: Core Web Vitals
Google's speed measurements boil down to three questions, called the Core Web Vitals:
| Measure | The question it answers | Good |
|---|---|---|
| Largest Contentful Paint (LCP) | How long until the main content appears? | 2.5 seconds or less |
| Interaction to Next Paint (INP) | When I tap something, how quickly does the page respond? | 200 milliseconds or less |
| Cumulative Layout Shift (CLS) | Does the page jump around while it loads? | 0.1 or less |
Lab tests and real visitors
There are two kinds of figures, and they often disagree:
- Lab tests (such as Google's PageSpeed Insights or Lighthouse) load the page once in a controlled, deliberately slow phone. They're repeatable, so they're good for spotting problems and checking a fix worked.
- Real-visitor figures (the Chrome User Experience Report) come from actual Chrome users over the last 28 days. They're what Google uses, but small sites may not have enough visitors to get them, and a fix takes weeks to show.
Use the lab test to find and fix problems, and the real-visitor figures to confirm the fix worked for people.
The fixes that matter most
In our experience, a handful of causes account for most slow phone sites.
- Oversized images. A 4,000-pixel photo shrunk to fit a phone screen still downloads at full size. Resize images to the largest size they're shown at, and use modern formats such as WebP or AVIF. This alone often halves the page weight.
- Too many scripts. Chat widgets, tracking pixels, sliders and page-builder extras all add JavaScript the phone must download and run. Remove what nobody uses, and load the rest after the main content.
- The main image loads late. If the large picture at the top is the page's main content, make sure it isn't lazy-loaded, and ask the browser to fetch it early (a "preload" hint).
- Slow server response. If the server takes a second just to start sending the page, nothing else can help. Page caching, a better hosting plan or a CDN usually fixes it.
- Web fonts. Several font families and weights add requests before text can appear. Use one or two, host them yourself, and let text show in a fallback font while they load.
- Things that jump. Images and adverts without a set width and height push text down as they load, which hurts CLS and annoys readers. Give every image its dimensions.
WordPress in particular
On WordPress, slow phone sites usually come down to too many plugins, a heavy page builder, or no caching. A caching plugin, an image optimisation plugin and a careful look at which plugins load scripts on every page will usually make the biggest difference.
Checking it stays fast
Speed tends to slip over time as pages, plugins and tracking scripts are added. TideStat runs Google's speed test on phones and computers on a schedule, shows the real-visitor figures next to it, and puts the biggest causes in the Fix list in plain words, so a slow month gets noticed before it shows up in your search traffic.
