Site speed and conversion rate - the numbers you need to know

Google has published data showing that for every additional second of mobile load time, conversion rate drops by up to 20 percent. Deloitte research found that a 0.1-second improvement in load time produced an 8 percent uplift in conversions for retail sites. These are not theoretical figures - they are measured outcomes from real traffic at scale. If your pages are slow, your paid search CPA is higher than it needs to be.

The Google Ads connection

Landing page experience is one of the three components of Quality Score in Google Ads. Page speed is a direct input into landing page experience. A slow landing page reduces your Quality Score, which reduces your Ad Rank, which means you either pay more per click to maintain position or lose positions to better-optimised competitors. Fixing page speed improves conversion rate and reduces CPC simultaneously. It is one of the highest-ROI technical investments in paid search.

Finding your baseline

Google PageSpeed Insights gives you a Core Web Vitals assessment for any URL. Run your key paid search landing pages - not just your homepage. Landing pages often have heavier JavaScript, more tracking pixels, and more dynamic content than standard pages, which can make them significantly slower. The Largest Contentful Paint score is the most important metric for conversion purposes - it measures how quickly the main content loads and strongly correlates with user experience.

The quick wins

Image optimisation is typically the highest-impact quick win. Uncompressed images are the most common reason for slow LCP scores. Convert images to WebP format, compress them to the minimum acceptable quality, and specify explicit width and height dimensions. Add lazy loading to images below the fold. These changes often take hours and can improve LCP scores significantly without any complex development work.

Render-blocking JavaScript

Scripts that load in the document head before the page content block rendering. Defer non-essential scripts, load analytics and tag manager asynchronously, and remove scripts no longer needed. Every script you remove from the critical rendering path improves speed. If your site runs 15 or 20 third-party scripts, audit them periodically and remove the ones no longer serving a purpose.