Website speed
Website speed refers to how quickly a web page loads and starts responding to user interactions. It's measured with Google's Core Web Vitals, which assess three key aspects: how fast the largest visible element loads (LCP), how responsive the page is to clicks and other interactions (INP), and how visually stable the layout is (CLS). A good result means LCP under 2.5 seconds, INP under 200 milliseconds, and CLS under 0.1.
Website speed has a direct, measurable impact on conversions, revenue, and user satisfaction. A slow website means real lost money:
- Every extra second costs conversions: a Portent study analyzing 100 million page views from 20 B2B and B2C websites found that an e-commerce site that loads in 1 second converts at 3.05%, while one that loads in 5 seconds converts at only 1.08%. For lead generation sites, the conversion rate drops from 39% to 18% as load time goes from 1 to 6 seconds (Portent – Site Speed Research)
- Milliseconds make millions: a Deloitte study for Google showed that an improvement of just 0.1 seconds increased conversions by 8.4% in e-commerce and by 10.1% in travel (Deloitte / Google – Milliseconds Make Millions, 2020)
- 53% of mobile users leave if a site doesn't load within 3 seconds. The probability of a bounce increases by 32% as load time goes from 1 to 3 seconds, and by 90% from 1 to 5 seconds (Think with Google – Mobile Page Speed Benchmarks)
- Real impact on sales: in an A/B test (about 100,000 clicks and 34,000 visits per day for each variant), Vodafone found that a 31% improvement in LCP led to 8% more online sales, a 15% improvement in lead conversion, and an 11% improvement in cart visits (web.dev – Vodafone Case Study)
FAQ
What are Core Web Vitals, and why do they matter?
Core Web Vitals are three Google metrics for assessing user experience: LCP (how fast the main content loads), INP (responsiveness to interactions, which replaced the earlier FID in March 2024), and CLS (visual stability). Google uses them as a ranking factor in search. According to case studies on web.dev, companies with a good LCP saw conversion rates up to 61% higher (web.dev – Core Web Vitals Business Impact).
How fast should a website be?
Google recommends an LCP under 2.5 seconds, but the data shows that faster is always better. A Portent study found that websites loading within 1 second have the highest conversion rates. According to research by Akamai and SOASTA (10 billion user visits to top retail websites), a delay of just 100 milliseconds causes a 7% drop in conversions (Akamai – State of Online Retail Performance, 2017).
How can you improve website speed?
Key steps include optimizing images (compression and modern formats like WebP and AVIF), minimizing render-blocking JavaScript, using a CDN for faster content delivery, and lazy loading elements outside the visible area. Vodafone achieved its 31% LCP improvement through exactly this kind of combination: optimizing SVG and PNG images, deferring the loading of off-screen elements, and switching to server-side rendering.
Sources:
- Portent – Site Speed & Revenue Research – analysis of 100 million page views from 20 B2B/B2C websites
- Deloitte / Google – Milliseconds Make Millions (2020) – 4-week study of retail and travel mobile sites
- Think with Google – Mobile Page Speed Benchmarks – research on mobile user behavior
- web.dev – Vodafone Case Study – A/B test with about 100K clicks and 34K visits per day
- Akamai / SOASTA – State of Online Retail Performance (2017) – data from 10 billion visits to top retail websites
- web.dev – Core Web Vitals Business Impact – collection of Core Web Vitals optimization case studies
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