Speed is easy to treat as a technical nicety. The research says otherwise: across retail, travel, publishing and lead generation, faster pages consistently convert better. Here are the studies worth knowing, what they do and do not prove, and a way to estimate the value for your own site.
The studies worth knowing
Deloitte: Milliseconds Make Millions
Commissioned by Google and published in 2020, this study tracked real mobile sites across retail, travel, luxury and lead generation. It found that a 0.1 second improvement in mobile site speed increased retail conversion rates by 8.4 percent and retail average order value by 9.2 percent. Travel sites saw a 10.1 percent lift in conversions.
Google: bounce probability and load time
Google's research on mobile landing pages found that as load time increases from one second to three seconds, the probability of a bounce rises by 32 percent. From one to five seconds, it rises by 90 percent.
Vodafone: a controlled A/B test
Vodafone ran an A/B test on a landing page, improving LCP by 31 percent in one version while keeping everything else the same. The faster version produced 8 percent more sales. Because it was a controlled test, it is one of the cleanest pieces of evidence that speed itself drives the result.
Rakuten 24: Core Web Vitals and revenue
In a case study published on web.dev, Rakuten 24 reported that improving its Core Web Vitals led to a 53 percent increase in revenue per visitor and a 33 percent increase in conversion rate in an A/B test.
Read results carefully
Why speed changes behavior
- Attention: every second of a blank or shifting screen is a moment for the visitor to go back to the search results.
- Trust: pages that jump, freeze or load in pieces feel broken, and people hesitate to enter card details on a page that feels broken.
- Momentum: each slow step in a checkout adds friction, and friction compounds over a multi-page flow.
- Mobile reality: many shoppers are on mid-range phones and patchy connections, where small inefficiencies become long waits.
Estimate what speed is worth to you
You do not need a perfect model. A rough estimate is enough to decide whether speed deserves budget.
Monthly revenue from organic + paid sessions = R
Expected conversion lift from faster pages = L (be conservative: 2% to 5%)
Estimated extra monthly revenue = R x L
Example:
R = $80,000 per month
L = 3%
Extra revenue = $80,000 x 0.03 = $2,400 per monthUse a deliberately conservative lift. If the number still justifies the work at three percent, you do not need to argue about whether it might really be eight.
Where to focus first
- Product and landing pages from ads, because you are paying for every visitor who bounces.
- Category or collection pages, which are often heavy with images and filters.
- Cart and checkout steps, where third-party scripts can delay buttons from responding.
- Your home page last. It is usually the best optimized page already.
Prove it on your own site
Split traffic between the current page and a faster version, or compare conversion rate for the same pages before and after a speed release, controlling for seasonality and campaigns. Segment results by device. The gains are almost always larger on mobile.
LightLoader is built to make that experiment easy: add one script, compare the weeks before and after, and judge it on revenue, not just a score.