The data is unambiguous
Few CRO claims are as well-evidenced as "speed matters." Google's 2018 study with Deloitte across 70 brands found a 0.1s mobile improvement lifted conversion 8.4%. Akamai's "milliseconds matter" research showed every 100ms of latency cuts ecommerce conversion 7%. Walmart, Pinterest, BBC, and Vodafone have all published similar findings.
Why speed compounds with everything else
Speed isn't only a conversion lever — it's a multiplier. A slow page loses visitors before they see your headline, so even a perfect headline can't help. A slow page can't rank well in Google, so you also lose the impressions you would have converted. A slow page burns more mobile data, so users learn to associate your brand with cost. Every other optimization works better on a fast page.
The cheapest win in CRO
Most pages can drop 1–2 seconds of LCP by compressing the hero image, deferring tracking scripts, and removing unused CSS — none of which require redesign work or copy changes. The page-speed guide walks through the order of operations. Run your page through PageSpeed to find the easy wins.