How to test if your website is fast on a phone

Test it in five minutes

1. Go to Google's PageSpeed Insights at pagespeed.web.dev.
2. Paste your website address and press Analyze.
3. Wait for the result and open the Mobile tab first, since most of your visitors use phones.
4. Read the score, then the list of things to fix underneath it.

Run it two or three times. The score moves a little on every run, so look for the pattern, not one number.

Two sets of numbers on one page

PageSpeed Insights shows two kinds of result, and they can disagree.

Visitor data comes from Chrome users who visited your page over the last 28 days. It shows what customers experience on their own phones and networks. A new or quiet website often has none, because Google needs enough visits before it reports anything.

The lab test loads your page once on a simulated phone and a slow connection. It is the 0 to 100 score. It is good for finding causes and weak at predicting what a particular customer sees.

If you have visitor data, trust it first. If you do not, the lab test is what you have.

What "good" means

Google's three Core Web Vitals each have a threshold, and at least three in four visits to the page must meet it.

A page passes only when all three are good.

What we found when we tested our own site

We ran this test on webstartindia.com. The first result was a mobile Performance score of 96 and a Largest Contentful Paint of 2.0 seconds. That is already green, and we wanted to know what was holding it back.

We made five copies of the page: one left as it was and four that each changed one suspect (the animations, the decorative layers, the font loading setting and the web fonts). We tested every copy with PageSpeed Insights. Only one change moved the result. With the web fonts removed, Largest Contentful Paint fell from 2.0 to 1.5 seconds.

So we kept the fonts and cut their weight, from about 87 KB to about 52 KB, by dropping weights and features the pages never use. The next test gave a mobile Performance score of 99, Largest Contentful Paint of 1.7 seconds, no blocking time and no layout shift.

Two things came out of that. First, guessing would have wasted days, because the animations and backgrounds we suspected were not the cause. Second, the biggest gain came from one change, not from a long list.

What usually slows a local business website

• Photos straight from a phone. A picture from a modern phone is often several megabytes, and the page may show it at a few hundred pixels wide. Resize and compress before upload.
• Plugins and scripts nobody remembers adding. Chat widgets, sliders, social feeds and tracking tags each add requests.
• Page builders that load everything on every page.
• Fonts and videos that load before the content.
• Hosting that answers slowly. Cheap shared hosting is often the cause when every page feels slow.

Test it like a customer

Open your website on your own phone using mobile data, not Wi-Fi. Count how long until you can read the first screen and tap a button. If you wait, your customers wait too, and many will leave.

What not to chase

A score of 100 is not the goal. A site that sits at 90 and answers a customer's question in the first screen does more for the business than one that scores 100 and has nothing to say. Fix what the report names first, run the test again and stop when the pages feel quick on a phone.

If you want help, see website redesign and speed optimization.

Sources

• PageSpeed Insights, Google.
• About PageSpeed Insights, Google for Developers.
• Web Vitals, web.dev.

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