In short: A slow website loses orders and rankings. Google measures the quality of a page with three figures: LCP (2.5 seconds or less), INP (200 milliseconds or less) and CLS (0.1 or less), assessed at the 75th percentile of real visitors. On a shop, the biggest factors are images, apps and plugins, third-party scripts, the theme and hosting.
Website speed isn't a techie's fad. Someone who opens a page on their phone and stares at a blank screen for a few seconds goes back. They don't get annoyed: they simply move on to a competitor. For an online shop, that means lost orders before anyone has even seen the product.
Three measurements that matter
Google has boiled the experience of a page down to three figures called Core Web Vitals. They're public, and you'll find them in PageSpeed Insights and Search Console.
- LCP (Largest Contentful Paint). The time it takes for the largest element on the page to appear: usually the main photo or the headline. A good value is 2.5 seconds or less.
- INP (Interaction to Next Paint). How long the page takes to respond to a tap or a click. A good value is 200 milliseconds or less.
- CLS (Cumulative Layout Shift). How much elements move around while the page loads. It's what makes you tap the wrong button because a banner has just appeared above it. A good value is 0.1 or less.
Measure with real visitor data, not just a lab test. The two results can be very different. Google looks at the 75th percentile of page loads, separately for mobile and desktop.
Where an online shop loses time
Images that are too heavy
This is the most common cause. A 4 MB photo loaded to be shown in a 400-pixel box wastes time everywhere. You need modern formats such as WebP or AVIF and sizes that suit the screen. Photos below the first screen should load later (lazy loading). The main one, on the other hand, should load straight away.
Too many apps and plugins
Every Shopify app and every WordPress plugin adds code. Many load it on every page, even where it isn't needed. Make a list of what you've installed. Ask yourself what each one actually delivers and switch off the rest. On WooCommerce, a forgotten plugin is often the culprit.
Third-party scripts
Chat, advertising pixels, maps, reviews and analytics tools load from external servers you don't control. Keep only the ones you need and have the others load once the customer interacts.
Theme and code
A theme that bundles ten libraries to use two of them weighs more than it needs to. This is development work: cutting the code sent to the browser, avoiding animations that block the page and loading fonts sensibly.
Hosting and caching
On WooCommerce the server matters. Good page caching and a well-kept database make a noticeable difference, especially at peak times such as promotions. On Shopify, this layer is handled by the platform.
A sensible order of work
- Measure the pages that bring in the most revenue: home page, main categories, product page and checkout.
- Compress and resize the images.
- Remove apps, plugins and scripts you don't need.
- Check the theme and the cache.
- Measure again and compare with your starting figures.
Speed and rankings
Core Web Vitals are among the signals Google takes into account when ranking pages. They don't replace good content: they stop it being held back. With relevance equal, a fast site starts with a small advantage. The surest gain, though, is with customers: people who don't have to wait buy more readily.
Further reading: hosting for a WooCommerce shop · maintaining a WordPress website · website care and maintenance
Frequently asked questions
What are good Core Web Vitals values?
An LCP of 2.5 seconds or less, an INP of 200 milliseconds or less and a CLS of 0.1 or less. The assessment uses the 75th percentile of page loads, separately for mobile and desktop.
What is INP?
Interaction to Next Paint: it measures how long the page takes to respond to a click or a tap. It replaced FID among the Core Web Vitals.
Where do you start when speeding up a shop?
With the pages that bring in the most revenue (home page, categories, product page, checkout). Then you compress the images, remove apps and scripts you don't need, check the theme and cache, and measure again.