Does your website load on a phone? Speed and mobile checks
Does the site load fast enough on a phone? 19 checks · 10% of the overall score.
Most visitors arrive on a phone, often on a mediocre connection. Google measures real-user loading, interactivity and layout stability (Core Web Vitals) and uses them as a ranking input; customers simply leave. This chapter combines our own measurements with Google's PageSpeed Insights where available.
The 19 checks
| Check | Why it matters |
|---|---|
| Server response time (TTFB) | Everything waits on the first byte; slow hosting caps every other optimisation. |
| Average response time across pages | One fast homepage can hide slow inner pages. |
| Total page weight | Multi-megabyte pages are slow on mobile data and expensive for visitors. |
| Text compression | Brotli/gzip cuts HTML, CSS and JS by 70%+ for free. |
| Cache headers on HTML | Sensible caching makes repeat visits instant. |
| HTTP/3 advertised | HTTP/3 improves performance on lossy mobile networks. |
| IPv6 enabled | Many mobile carriers are IPv6-first; missing AAAA records add latency. |
| Mobile viewport | Without a viewport meta tag the page renders as a shrunken desktop. |
| Legible font sizes on mobile | Text under 12px forces zooming and fails Google's mobile check. |
| Tap targets sized for fingers | Tiny, crowded links cause mis-taps and frustration. |
| Modern image formats / lazy loading | WebP/AVIF and loading=lazy are the biggest weight savings on most sites. |
| Image optimisation opportunity | Oversized images are the number one cause of slow small-business sites. |
| Render-blocking resources | CSS and JS in the head delay the first paint. |
| Unused JavaScript / CSS | Shipping code that never runs is pure cost. |
| Third-party script domains | Each external script is a performance and privacy liability. |
| WordPress plugins loading on homepage | Plugin sprawl is the classic WordPress slowdown. |
| Text-to-HTML ratio | Very low ratios indicate bloated markup or thin content. |
| Lighthouse performance (mobile) | Google's lab score on a simulated mid-range phone. |
| Real-user Core Web Vitals (28 days) | What actual Chrome users experienced — the numbers Google ranks with. |
Most common fixes
- Compress and resize images; serve WebP or AVIF; add loading="lazy" below the fold.
- Enable compression and a CDN at the host; upgrade hosting if TTFB is over 600 ms.
- Remove unused plugins and third-party scripts; defer the rest.
- Ensure a viewport meta tag and a 16px base font size.
Questions
What are Core Web Vitals?
Three metrics Google collects from real Chrome users: Largest Contentful Paint (loading), Interaction to Next Paint (responsiveness) and Cumulative Layout Shift (visual stability). Passing all three is a ranking factor and a conversion factor.
How fast should my website load?
Aim for a server response under 600 ms and Largest Contentful Paint under 2.5 seconds on mobile. Most small-business sites fail the second one because of oversized images.