Your store is not slow to you. It is slow to the person about to buy
Your store feels fine on your phone because your browser cached it. Here is how Google actually measures speed, where the time really goes in a store, and the fix order that works.
By Yannis Spanenburg · · 6 min read
Open your own store on your own phone and it feels fine. That is the trap. Your browser has cached the whole thing, you are on good wifi, and you are not the customer standing in a doorway on a three year old Android with two bars of signal. That person is the one whose experience gets measured.
What fast enough actually means
Google defines three thresholds. Largest Contentful Paint under 2.5 seconds, so the main content appears quickly. Interaction to Next Paint under 200 milliseconds, so taps respond. Cumulative Layout Shift under 0.1, so nothing jumps while someone is reaching for a button. Clear all three for most visitors and your site is fast enough.
Two details matter more than the numbers themselves. These are measured on real visits rather than on your machine, and you are graded at the 75th percentile. Three quarters of your visitors need a good experience to pass, which means the slowest quarter of your traffic decides your result.
Why your Lighthouse score disagrees with Search Console
Lighthouse runs a simulation on demand. Search Console reports what actually happened to real people over the previous 28 days. A store can score in the nineties in the lab and still fail in the field, usually because real customers arrive on worse devices and worse connections than any test assumes.
When the two disagree, the field data wins. It is the one Google uses.
Where the time actually goes in a store
Apps you installed and forgot
Every app that adds a widget adds JavaScript, and most of it loads on every page rather than only the page it serves. A review widget running on checkout, a currency converter running on the blog, an upsell script on a page with nothing to upsell. Uninstalling an app does not reliably remove its code from the theme either.
Images that were never resized
A product photo exported at 3000 pixels wide and displayed at 600 is the most common single problem in ecommerce. Serve modern formats, size images to the space they actually occupy, and give every one explicit dimensions so the layout stops jumping while they load.
Third-party tags nobody can name
Analytics, pixels, chat widgets, heatmaps and consent scripts all queue up before your customer can do anything. Most stores have accumulated more of these than anyone still remembers approving. Auditing that list is usually faster and cheaper than optimising code you wrote yourself.
Does speed actually change sales?
Yes, though not for the reason the famous statistic claims. You have seen the line about one second costing a fixed percentage of conversions. It gets quoted constantly, sourced almost never, and it does not transfer cleanly between businesses. Treat any universal number here with suspicion.
The honest mechanism is simpler. Slow pages get abandoned before they finish rendering, so those visits never enter your funnel to be counted. Speed is a real if modest ranking signal, so it compounds with everything else you do. And paid traffic pays twice for a slow landing page, once for the click and again for the bounce.
The fix order that works
Measure the field data first, not the lab score. Then remove before you optimise: unused apps, duplicate tags, fonts nobody is using. Then fix images. Then defer whatever is left that does not need to run immediately. Rewriting code comes last, and for most stores it never needs to come at all.
Most stores do not need to be made faster. They need to have less done to them.
Your first two moves
Open Search Console, find the Core Web Vitals report, and look at the mobile tab. That is your real score. Then open your theme and count the third-party scripts loading on your homepage. If that number surprises you, you have found your project, and it is a deletion project rather than a development one.
Frequently asked questions
What is a good page speed for an ecommerce site?
Largest Contentful Paint under 2.5 seconds, Interaction to Next Paint under 200 milliseconds, and Cumulative Layout Shift under 0.1. These are measured on real visits at the 75th percentile, so three quarters of your visitors need to hit those numbers for the page to pass.
Why is my Lighthouse score high but Google says my site is slow?
Lighthouse is a lab simulation run on demand from your machine. Google's ranking data comes from field measurements of real visits over the previous 28 days, on the devices and connections your actual customers use. When the two disagree, the field data is the one that counts.
Do Shopify apps slow down my store?
Usually yes. Most apps inject JavaScript that loads on every page rather than only where the app is used, and uninstalling an app does not always remove its leftover code from your theme. Auditing your installed apps is often the single fastest speed improvement available to a store.
Does site speed affect Google rankings?
It is a genuine ranking signal but a modest one. Relevance and content quality still decide far more. Speed is best understood as a multiplier on everything else you do rather than a shortcut to ranking on its own.
How much revenue does a slow website cost?
There is no reliable universal figure, and the widely quoted one about a single second costing a fixed percentage of conversions is rarely sourced properly. The measurable effects are abandonment before the page renders, a modest ranking penalty, and paid traffic that bounces after you have already paid for the click.