Page speed is the CRO lever most teams treat as an engineering problem rather than a conversion problem. That's a category error. Load time is part of the visitor's experience from the first second — and it sets the tone for everything that follows.
What loads fast converts better. Speed isn't an engineering metric — it's a conversion metric.
The best surveyed landing page converts at 26.50% against an industry average of 7.20% — a 3.5× performance gap. The difference between a good page and a great one isn't a single tactic. But slow load times are consistently found in the bottom quartile, not the top. — 2026 Growth Marketer Survey
What the Research Says About Load Time and Conversion
Studies consistently show that every additional second of load time reduces conversion rate by 4–7% on average. On mobile, the effect is larger — and given that mobile conversion already lags desktop by nearly 3 percentage points (4.41% vs. 7.33%), slow mobile load times compound an existing gap into a serious problem.
The relationship isn't linear. The most damaging jump is from under 2 seconds to over 3 seconds. Pages that load in under 1.5 seconds on mobile see a meaningful conversion advantage over pages in the 3–5 second range, even when all other variables are held constant.
The Most Common Speed Problems on Landing Pages
When auditing landing pages for speed, these four issues appear most frequently:
- Unoptimised images: hero images over 300KB, no WebP format, no lazy loading below the fold
- Render-blocking scripts: third-party tracking scripts, chat widgets, and A/B testing SDKs loading synchronously in the head
- No CDN: assets served from the origin server rather than a CDN edge node close to the visitor
- Excessive font loading: importing four weights of a variable font when only two are used on the page
Speed as a Testing Variable
Page speed is rarely tested directly — but it should be. A variant that removes a heavy image in the hero or defers a render-blocking script can be run as a standard A/B test with conversion rate as the primary metric and Core Web Vitals as a secondary metric.
This is especially valuable on mobile, where the performance gap is largest and the effort to close it — progressive image loading, deferred scripts, a lightweight hero — is relatively low. The conversion lift from fixing mobile load time often exceeds the lift from copy or design experiments on the same page.
Where to Start
Run PageSpeed Insights on your highest-traffic landing page. Look at the mobile score. If it's below 70, your first test hypothesis should be a performance-focused variant — not a copy change, not a new CTA, not a layout shuffle. Fix the floor before you optimise for the ceiling.