How your Shopify store's speed affects your sales

In e-commerce, speed isn't a technical detail — it's a commercial one. Every second before your page renders, some share of your visitors closes the tab. That loss comes straight out of your ad budget: you pay for the traffic but your site is too slow to convert it.

Which metrics actually matter?

Google's Core Web Vitals capture perceived speed in three numbers. They affect both your search ranking and your conversion rate directly.

• LCP (largest contentful paint): under 2.5 seconds — usually your hero or product image
• INP (interaction to next paint): under 200 ms — the lag after someone taps add-to-cart
• CLS (cumulative layout shift): under 0.1 — buttons jumping around as the page loads

What slows a Shopify store down most?

The causes we find in the field come up in almost the same order every time: too many installed apps, unoptimised images, and dead code accumulating inside the theme.

Apps are the most insidious of the three. Every app you install injects its own JavaScript into the storefront, and when you uninstall it that code often stays behind in the theme. Six months later, five apps you no longer use may still be downloading on every single page view.

Audit your installed apps regularly. Every app you aren't using is a speed tax you're still paying.

Images: the fastest win available

In most stores images account for the bulk of total page weight. Modern formats (WebP, AVIF), correct sizing and lazy loading for anything below the fold will often improve LCP by whole seconds on their own. Shopify's own image transformation pipeline automates most of this — provided the theme uses it properly.

Don't optimise what you haven't measured

A Lighthouse score is a starting point, but it measures lab conditions. For what your real customers experience, follow Shopify's Web Performance report and the Core Web Vitals data in Google Search Console. What happens on a mid-range phone over a slow connection matters far more than the speed you see on your own desktop.

When is it time to rebuild the theme?

Sometimes optimisation isn't enough. A theme that has been edited for years by several different developers can carry so much technical debt that rebuilding is faster and cheaper than cleaning up. Use this test when deciding: if the cost of getting the current theme to your target is approaching the cost of building a new one, rebuild.