Page load time is the total elapsed time from when a visitor navigates to your URL to when the page is fully rendered and interactive. But "fully loaded" is a blurry concept — technically, a page isn't "done" until every last tracking pixel and deferred script finishes. That's why the industry has moved toward specific milestones (FCP, LCP, TTI) rather than a single load time number.
That said, the overall correlation is clear and well-documented: pages loading in 1-2 seconds convert 2-3x better than pages loading in 5+ seconds. Amazon famously found that every 100ms of added latency cost them 1% of revenue. Your landing page isn't Amazon, but the principle scales — faster pages hold attention, and attention converts.
What to actually measure
Don't rely on a single number. Track LCP (when main content is visible), TTI (when the page is interactive), and total page weight (in MB). A page can "load" in 2 seconds visually but not be interactive for 5 seconds because JavaScript is still executing. That gap is where visitors click your CTA and nothing happens.
For landing pages running paid traffic, calculate the cost of slow loading: if you spend $10/click and 20% of visitors leave before the page loads, you're burning $2 per abandoned click. At 1,000 clicks per month, that's $2,000 wasted on visitors who never saw your offer. Speed optimization has direct, calculable ROI.