How to test and speed up your website on mobile
Yeheli Sampson · · 3 min read
The short answer
Test your site at pagespeed.web.dev on the Mobile tab. Look at three metrics: LCP (main content load, good up to 2.5 seconds), INP (response to taps, good up to 200 milliseconds) and CLS (layout shift, good up to 0.1). Fix heavy images, unneeded scripts, fonts and first-screen video first.
Most of a small business's customers arrive on a phone, often on the move with a patchy connection. A slow site loses them before they read the headline. Google also takes page experience into account when ranking.
This guide shows how to test your site yourself, how to read the results, and what to fix first.
Step 1: Test the site
- 1
Open PageSpeed Insights
Go to pagespeed.web.dev, paste your site's address and click Analyze.
- 2
Switch to the Mobile tab
That is the result that matters, because most visitors arrive on a phone.
- 3
Test inner pages too
Not only the home page. A heavy service page can be slow even when the home page is fast.
A human test matters just as much: open your site on a phone over mobile data, not home Wi-Fi, and notice how long it takes to see the headline and the button.
Step 2: Understand the three metrics
Google measures page experience with three metrics called Core Web Vitals:
- LCP: how long the main content on screen takes to load. Good: up to 2.5 seconds.
- INP: how fast the page responds to taps and typing. Good: up to 200 milliseconds.
- CLS: how much the page jumps while loading. Good: up to 0.1.
Below the metrics, PageSpeed lists opportunities to improve. You do not need to understand every line. Start from the top of the list.
Step 3: Fix the images
Images are the most common reason for a slow site. A photo taken on a phone and uploaded as is can weigh several megabytes, while the site shows it far smaller.
- Resize each image to the size it is actually shown at
- Save in a modern format such as WebP or AVIF
- Load images below the first screen only when they are reached (lazy loading)
- Set a width and height on every image so the page does not jump
<img src="studio.webp" width="800" height="600" loading="lazy" alt="The studio inside">Step 4: Remove unneeded scripts
Every plugin, chat widget, pixel and animation adds code the phone has to download and run. Go through the list and keep only what is really used.
A good question for each plugin: if it disappeared tomorrow, would anyone notice?
Step 5: Fonts
Every font and every weight is another file. Pick one or two fonts, only the weights you use, and only the scripts you need (for example Hebrew and Latin).
Step 6: Video on the first screen
A big background video looks impressive, but on a phone it can be the heaviest thing on the page. If you keep it, compress it well, add a poster image, and consider swapping it for an image on mobile.
Step 7: Hosting
Good hosting with a content delivery network (CDN) serves the site from a server close to the visitor. Static sites have very fast hosting options today.
Fast is not enough: easy too
- Text large enough to read without zooming
- Buttons big enough to tap with a thumb
- The WhatsApp button visible without scrolling
- No pop-ups hiding the content
Questions on this topic
What is a good PageSpeed score?
The score is an indication. It matters more to look at the three metrics (LCP, INP, CLS) and make sure they are in the good range, especially on mobile.
The site feels fast to me, why is the score low?
On your phone the site may be cached and on a fast network. The test simulates a first-time visitor with an average phone on mobile data.
Does speed affect Google?
Google takes page experience into account, including these metrics. Just as important, visitors do not leave before the page loads.